... is an enhanced but completely compatible version of the Berkeley UNIX
C shell, It is a command language interpreter usable both as an interactive
login shell and a shell script command processor. It includes a command-
line editor (see programmable word completion (see spelling correction (see
a history mechanism (see job control (see and a C-like syntax. The section
describes major enhancements of over Throughout this manual, features of
not found in most implementations (specifically, the 4.4BSD are labeled
with and features which are present in but not usually documented are
labeled with If the first argument (argument 0) to the shell is then it is
a login shell. A login shell can be also specified by invoking the shell
with the flag as the only argument. The rest of the flag arguments are
interpreted as follows: Forces a from option processing, causing any
further shell arguments to be treated as non-option arguments. The
remaining arguments will not be interpreted as shell options. This may be
used to pass options to a shell script without confusion or possible
subterfuge. The shell will not run a set-user ID script without this
option. Commands are read from the following argument (which must be
present, and must be a single argument), stored in the shell variable for
reference, and executed. Any remaining arguments are placed in the shell
variable. The shell loads the directory stack from as described under
whether or not it is a login shell. (+) Sets the environment variable to
(Domain/OS only) (+) The shell exits if any invoked command terminates
abnormally or yields a non-zero exit status. The shell does not load any
resource or startup files, or perform any command hashing, and thus starts
faster. The shell uses instead of to spawn processes. (+) The shell is
interactive and prompts for its top-level input, even if it appears to not
be a terminal. Shells are interactive without this option if their inputs
and outputs are terminals. The shell is a login shell. Applicable only if
is the only flag specified. The shell loads even if it does not belong to
the effective user. Newer versions of can pass to the shell. (+) The shell
parses commands but does not execute them. This aids in debugging shell
scripts. The shell accepts SIGQUIT (see and behaves when it is used under
a debugger. Job control is disabled. (u) Command input is taken from the
standard input. The shell reads and executes a single line of input. A
may be used to escape the newline at the end of this line and continue onto
another line. Sets the shell variable, so that command input is echoed
after history substitution. Sets the shell variable, so that commands are
echoed immediately before execution. Sets the shell variable even before
executing Is to as is to Print a help message on the standard output and
exit. (+) Print the version/platform/compilation options on the standard
output and exit. This information is also contained in the shell variable.
(+) After processing of flag arguments, if arguments remain but none of the
or options were given, the first argument is taken as the name of a file of
commands, or to be executed. The shell opens this file and saves its name
for possible resubstitution by Because many systems use either the standard
version 6 or version 7 shells whose shell scripts are not compatible with
this shell, the shell uses such a shell to execute a script whose first
character is not a i.e., that does not start with a comment. Remaining
arguments are placed in the shell variable. A login shell begins by
executing commands from the system files and It then executes commands from
files in the user's directory: first or, if is not found, then the contents
of (or the value of the shell variable) are loaded into memory, then and
finally (or the value of the shell variable) (+). The shell may read
before instead of after and before instead of after or and if so compiled;
see the shell variable. (+) Non-login shells read only and or on startup.
For examples of startup files, please consult: Commands like and which need
be run only once per login, usually go in one's file. Users who need to
use the same set of files with both and can have only a which checks for
the existence of the shell variable before using -specific commands, or can
have both a and a which s (see the builtin command) The rest of this manual
uses to mean or, if is not found, In the normal case, the shell begins
reading commands from the terminal, prompting with (Processing of arguments
and the use of the shell to process files containing command scripts are
described later.) The shell repeatedly reads a line of command input,
breaks it into words, places it on the command history list, parses it and
executes each command in the line. One can log out by typing on an empty
line, or or via the shell's autologout mechanism (see the shell variable).
When a login shell terminates it sets the shell variable to or as
appropriate, then executes commands from the files and The shell may drop
DTR on logout if so compiled; see the shell variable. The names of the
system login and logout files vary from system to system for compatibility
with different variants; see We first describe The and sections describe
two sets of functionality that are implemented as editor commands but which
deserve their own treatment. Finally, lists and describes the editor
commands specific to the shell and their default bindings. Command-line
input can be edited using key sequences much like those used in or The
editor is active only when the shell variable is set, which it is by
default in interactive shells. The builtin can display and change key
bindings to editor commands (see -style key bindings are used by default
(unless the shell was compiled otherwise; see the shell variable), but can
change the key bindings to -style bindings en masse. The shell always
binds the arrow keys (as defined in the environment variable) to editor
commands: unless doing so would alter another single-character binding.
One can set the arrow key escape sequences to the empty string with to
prevent these bindings. The ANSI/VT100 sequences for arrow keys are always
bound. Other key bindings are, for the most part, what and users would
expect and can easily be displayed by so there is no need to list them
here. Likewise, can list the editor commands with a short description of
each. Certain key bindings have different behavior depending if or -style
bindings are being used; see for more information. Note that editor
commands do not have the same notion of a as does the shell. The editor
delimits words with any non-alphanumeric characters not in the shell
variable while the shell recognizes only whitespace and some of the
characters with special meanings to it, listed under The shell is often
able to complete words when given a unique abbreviation. For example,
typing part of a word and hit the tab key to run the editor command. The
shell completes the filename to replacing the incomplete word with the
complete word in the input buffer. (Note the terminal completion adds a to
the end of completed directories and a space to the end of other completed
words, to speed typing and provide a visual indicator of successful
completion. The shell variable can be unset to prevent this.) If no match
is found (perhaps doesn't exist), the terminal bell rings. If the word is
already complete (perhaps there is a on your system, or perhaps you were
thinking too far ahead and typed the whole thing) a or space is added to
the end if it isn't already there. Completion works anywhere in the line,
not at just the end; completed text pushes the rest of the line to the
right. Completion in the middle of a word often results in leftover
characters to the right of the cursor that need to be deleted. Commands
and variables can be completed in much the same way. For example, typing
would complete to if were the only command on your system beginning with
Completion can find a command in any directory in or if given a full
pathname. Typing would complete to if no other variable began with The
shell parses the input buffer to determine whether the word you want to
complete should be completed as a filename, command or variable. The first
word in the buffer and the first word following or is considered to be a
command. A word beginning with is considered to be a variable. Anything
else is a filename. An empty line is as a filename. You can list the
possible completions of a word at any time by typing to run the editor
command. The shell lists the possible completions using the builtin and
reprints the prompt and unfinished command line, for example: > ls
/usr/l[^D] lbin/ lib/ local/ lost+found/ > ls /usr/l If
the shell variable is set, the shell lists the remaining choices (if any)
whenever completion fails: > set autolist > nm /usr/lib/libt[tab]
libtermcap.a@ libtermlib.a@ > nm /usr/lib/libterm If the shell variable is
set to choices are listed only when completion fails and adds no new
characters to the word being completed. A filename to be completed can
contain variables, your own or others' home directories abbreviated with
(see and directory stack entries abbreviated with (see For example, > ls
~k[^D] kahn kas kellogg > ls ~ke[tab] > ls ~kellogg/ or > set local
= /usr/local > ls $lo[tab] > ls $local/[^D] bin/ etc/ lib/ man/ src/ > ls
$local/ Note that variables can also be expanded explicitly with the editor
command. lists at only the end of the line; in the middle of a line it
deletes the character under the cursor and on an empty line it logs one out
or, if the variable is set, does nothing. bound to the editor command
lists completion possibilities anywhere on a line, and (or any one of the
related editor commands that do or don't delete, list and/or log out,
listed under can be bound to with the builtin command if so desired. The
and editor commands (not bound to any keys by default) can be used to cycle
up and down through the list of possible completions, replacing the current
word with the next or previous word in the list. The shell variable can be
set to a list of suffixes to be ignored by completion. Consider the
following: > ls Makefile condiments.h~ main.o side.c
README main.c meal side.o condiments.h
main.c~ > set fignore = (.o \~) > emacs ma[^D] main.c main.c~ main.o >
emacs ma[tab] > emacs main.c and are ignored by completion (but not
listing), because they end in suffixes in Note that a was needed in front
of to prevent it from being expanded to as described under is ignored if
only one completion is possible. If the shell variable is set to
completion 1) ignores case and 2) considers periods, hyphens and
underscores and to be word separators and hyphens and underscores to be
equivalent. If you had the following files comp.lang.c comp.lang.perl
comp.std.c++ comp.lang.c++ comp.std.c and typed it would be completed to
and typing would list and Typing would list and Typing in the following
directory A_silly_file a-hyphenated-file another_silly_file would
list all three files, because case is ignored and hyphens and underscores
are equivalent. Periods, however, are not equivalent to hyphens or
underscores. If the shell variable is set to completion ignores case and
differences between a hyphen and an underscore word separator only when the
user types a lowercase character or a hyphen. Entering an uppercase
character or an underscore will not match the corresponding lowercase
character or hyphen word separator. Typing in the directory of the
previous example would still list all three files, but typing would match
only and typing would match just and because the user explicitly used an
uppercase or an underscore character. Completion and listing are affected
by several other shell variables: can be set to complete on the shortest
possible unique match, even if more typing might result in a longer match:
> ls fodder foo food foonly > set recexact > rm fo[tab] just
beeps, because could expand to or but if we type another > rm foo[tab] > rm
foo the completion completes on even though and also match. can be set to
run the editor command before each completion attempt, can be set to
spelling-correct the word to be completed (see before each completion
attempt and can be set to complete commands automatically after one hits
return. can be set to make completion beep or not beep in a variety of
situations, and can be set to never beep at all. can be set to a list of
directories and/or patterns that match directories to prevent the
completion mechanism from ing those directories. and can be set to limit
the number of items and rows (respectively) that are listed without asking
first. can be set to make the shell list only executables when listing
commands, but it is quite slow. Finally, the builtin command can be used
to tell the shell how to complete words other than filenames, commands and
variables. Completion and listing do not work on glob-patterns (see but
the and editor commands perform equivalent functions for glob-patterns.
The shell can sometimes correct the spelling of filenames, commands and
variable names as well as completing and listing them. Individual words
can be spelling-corrected with the editor command (usually bound to and and
the entire input buffer with (usually bound to The shell variable can be
set to to correct the command name or to correct the entire line each time
return is typed, and can be set to correct the word to be completed before
each completion attempt. When spelling correction is invoked in any of
these ways and the shell thinks that any part of the command line is
misspelled, it prompts with the corrected line: > set correct = cmd > lz
/usr/bin CORRECT>ls /usr/bin (y|n|e|a)? One can answer or space to execute
the corrected line, to leave the uncorrected command in the input buffer,
to abort the command as if had been hit, and anything else to execute the
original line unchanged. Spelling correction recognizes user-defined
completions (see the builtin command). If an input word in a position for
which a completion is defined resembles a word in the completion list,
spelling correction registers a misspelling and suggests the latter word as
a correction. However, if the input word does not match any of the
possible completions for that position, spelling correction does not
register a misspelling. Like completion, spelling correction works
anywhere in the line, pushing the rest of the line to the right and
possibly leaving extra characters to the right of the cursor. lists key
bindings and lists and briefly describes editor commands. Only new or
especially interesting editor commands are described here. See and for
descriptions of each editor's key bindings. The character or characters to
which each command is bound by default is given in parentheses. means a
control character and a meta character, typed as (or on terminals without a
meta key. Case counts, but commands that are bound to letters by default
are bound to both lower- and uppercase letters for convenience. Supported
editor commands are: Move back a character. Cursor behavior modified by
Cut from beginning of current word to cursor - saved in cut buffer. Word
boundary behavior modified by Move to beginning of current word. Word
boundary and cursor behavior modified by Move to beginning of line. Cursor
behavior modified by Capitalize the characters from cursor to end of
current word. Word boundary behavior modified by Completes a word as
described under Like but steps up from the end of the list. Replaces the
current word with the first word in the list of possible completions. May
be repeated to step down through the list. At the end of the list, beeps
and reverts to the incomplete word. Like but ignores user-defined
completions. Copies the previous word in the current line into the input
buffer. See also Word boundary behavior modified by Expands the current
word to the most recent preceding one for which the current is a leading
substring, wrapping around the history list (once) if necessary. Repeating
without any intervening typing changes to the next previous word etc.,
skipping identical matches much like does. Deletes the character under the
cursor. See also Cursor behavior modified by Does if there is a character
under the cursor or on an empty line. See also Cursor behavior modified by
Does if there is a character under the cursor or at the end of the line.
See also Does if there is a character under the cursor, at the end of the
line or on an empty line. See also those three commands, each of which
does only a single action, and and each of which does a different two out
of the three. Cut from cursor to end of current word - save in cut buffer.
Word boundary behavior modified by Like but steps down, stopping at the
original input line. Lowercase the characters from cursor to end of
current word. Word boundary behavior modified by Signals an end of file,
causing the shell to exit unless the shell variable is set to prevent this.
See also Move cursor to end of line. Cursor behavior modified by Expands
history substitutions in the current word. See See also and the shell
variable. Expands the glob-pattern to the left of the cursor. See Like
but expands history substitutions in each word in the input buffer.
Expands the variable to the left of the cursor. See Move forward one
character. Cursor behavior modified by Move forward to end of current
word. Word boundary and cursor behavior modified by Searches backwards
through the history list for a command beginning with the current contents
of the input buffer up to the cursor and copies it into the input buffer.
The search string may be a glob-pattern (see containing or and will proceed
from the appropriate point in the history list. Emacs mode only. See also
and Like but searches forward. Searches backward like copies the first
match into the input buffer with the cursor positioned at the end of the
pattern, and prompts with and the first match. Additional characters may
be typed to extend the search, may be typed to continue searching with the
same pattern, wrapping around the history list if necessary, must be bound
to a single character for this to work) or one of the following special
characters may be typed: Appends the rest of the word under the cursor to
the search pattern. Undoes the effect of the last character typed and
deletes a character from the search pattern if appropriate. If the
previous search was successful, aborts the entire search. If not, goes
back to the last successful search. Ends the search, leaving the current
line in the input buffer. Any other character not bound to terminates the
search, leaving the current line in the input buffer, and is then
interpreted as normal input. In particular, a carriage return causes the
current line to be executed. See also and Word boundary behavior modified
by Like but searches forward. Word boundary behavior modified by Inserts
the last word of the previous input line into the input buffer. See also
Lists completion possibilities as described under See also and Like but
ignores user-defined completions. Lists (via the builtin) matches to the
glob-pattern (see to the left of the cursor. Does or on an empty line.
See also Expands history substitutions in the current line, like and
inserts a space. is designed to be bound to the space bar, but is not
bound by default. Searches for the current word in and, if it is found,
replaces it with the full path to the executable. Special characters are
quoted. Aliases are expanded and quoted but commands within aliases are
not. This command is useful with commands that take commands as arguments,
e.g., and Expands the current word as described under the setting of the
shell variable. Toggles between input and overwrite modes. Saves the
current input line and looks for a stopped job where the file name portion
of its first word is found in the shell variable. If is not set, then the
file name portion of the environment variable if unset) and the environment
variable if unset) will be used. If such a job is found, it is restarted
as if had been typed. This is used to toggle back and forth between an
editor and the shell easily. Some people bind this command to so they can
do this even more easily. Searches for documentation on the current
command, using the same notion of as the completion routines, and prints
it. There is no way to use a pager; is designed for short help files. If
the special alias is defined, it is run with the command name as a sole
argument. Else, documentation should be in a file named or which should be
in one of the directories listed in the environment variable. If there is
more than one help file only the first is printed. In insert mode (the
default), inserts the typed character into the input line after the
character under the cursor. In overwrite mode, replaces the character
under the cursor with the typed character. The input mode is normally
preserved between lines, but the shell variable can be set to or to put the
editor in that mode at the beginning of each line. See also Indicates that
the following characters are part of a multi-key sequence. Binding a
command to a multi-key sequence really creates two bindings: the first
character to and the whole sequence to the command. All sequences
beginning with a character bound to are effectively bound to unless bound
to another command. Attempts to correct the spelling of each word in the
input buffer, like but ignores words whose first character is one of or or
which contain or to avoid problems with switches, substitutions and the
like. See Attempts to correct the spelling of the current word as
described under Checks each component of a word which appears to be a
pathname. Expands or unexpands history substitutions in the input buffer.
See also and the shell variable. Beeps. Copies the previous entry in the
history list into the input buffer. If is set, uses the literal form of
the entry. May be repeated to step up through the history list, stopping
at the top. Uppercase the characters from cursor to end of current word.
Word boundary behavior modified by Vi goto the beginning of next word.
Word boundary and cursor behavior modified by Vi move to the end of the
current word. Word boundary behavior modified by Prompts with for a search
string (which may be a glob-pattern, as with searches for it and copies it
into the input buffer. The bell rings if no match is found. Hitting
return ends the search and leaves the last match in the input buffer.
Hitting escape ends the search and executes the match. mode only. Like
but searches forward. Does a (see the description of the builtin command)
on the first word of the input buffer. When executed immediately after a
or another replaces the yanked string with the next previous string from
the killring. This also has the effect of rotating the killring, such that
this string will be considered the most recently killed by a later command.
Repeating will cycle through the killring any number of times. The shell
splits input lines into words at blanks and tabs. The special characters
and and the doubled characters and are always separate words, whether or
not they are surrounded by whitespace. When the shell's input is not a
terminal, the character is taken to begin a comment. Each and the rest of
the input line on which it appears is discarded before further parsing. A
special character (including a blank or tab) may be prevented from having
its special meaning, and possibly made part of another word, by preceding
it with a backslash or enclosing it in single double or backward quotes.
When not otherwise quoted a newline preceded by a is equivalent to a blank,
but inside quotes this sequence results in a newline. Furthermore, all
except can be prevented by enclosing the strings (or parts of strings) in
which they appear with single quotes or by quoting the crucial character(s)
(e.g., or for or respectively) with is no exception: quoting in any way any
character of a word for which an has been defined prevents substitution of
the alias. The usual way of quoting an alias is to precede it with a
backslash.) is prevented by backslashes but not by single quotes. Strings
quoted with double or backward quotes undergo and but other substitutions
are prevented. Text inside single or double quotes becomes a single word
(or part of one). Metacharacters in these strings, including blanks and
tabs, do not form separate words. Only in one special case (see can a
double-quoted string yield parts of more than one word; single-quoted
strings never do. Backward quotes are special: they signal which may
result in more than one word. C-style escape sequences can be used in
single quoted strings by preceding the leading quote with (+) See for a
complete list of recognized escape sequences. Quoting complex strings,
particularly strings which themselves contain quoting characters, can be
confusing. Remember that quotes need not be used as they are in human
writing! It may be easier to quote not an entire string, but only those
parts of the string which need quoting, using different types of quoting to
do so if appropriate. The shell variable can be set to make backslashes
always quote and (+). This may make complex quoting tasks easier, but it
can cause syntax errors in scripts. The following escape sequences are
always recognized inside a string constructed using and optionally by the
builtin command as controlled by the shell variable. Supported escape
sequences are: Bell. Backspace. The control character denoted by in If is
a backslash, it must be doubled. Escape. Form feed. Newline. Carriage
return. Horizontal tab. Vertical tab. Literal backslash. Literal single
quote. Literal double quote. The character corresponding to the octal
number The character corresponding to the hexadecimal number (1-2
hexadecimal digits). The character corresponding to the hexadecimal number
(1-8 hexadecimal digits). The Unicode code point (1-4 hexadecimal digits).
The Unicode code point (1-8 hexadecimal digits). The implementations of
and in other shells may take a varying number of digits. It is often
safest to use leading zeros to provide the maximum expected number of
digits. We now describe the various transformations the shell performs on
the input in the order in which they occur. We note in passing the data
structures involved and the commands and variables which affect them.
Remember that substitutions can be prevented by quoting as described under
Each command, or input from the terminal is saved in the history list. The
previous command is always saved, and the shell variable can be set to a
number to save that many commands. The shell variable can be set to not
save duplicate events or consecutive duplicate events. Saved commands are
numbered sequentially from 1 and stamped with the time. It is not usually
necessary to use event numbers, but the current event number can be made
part of the prompt by placing an in the shell variable. By default history
entries are displayed by printing each parsed token separated by space;
thus the redirection operator will be displayed as The shell actually saves
history in expanded and literal (unexpanded) forms. If the shell variable
is set, commands that display and store history use the literal form. The
builtin command can print, store in a file, restore and clear the history
list at any time, and the and shell variables can be set to store the
history list automatically on logout and restore it on login. History
substitutions introduce words from the history list into the input stream,
making it easy to repeat commands, repeat arguments of a previous command
in the current command, or fix spelling mistakes in the previous command
with little typing and a high degree of confidence. History substitutions
begin with the character They may begin anywhere in the input stream, but
they do not nest. The may be preceded by a to prevent its special meaning;
for convenience, a is passed unchanged when it is followed by a blank, tab,
newline, or History substitutions also occur when an input line begins with
see The characters used to signal history substitution and can be changed
by setting the shell variable. Any input line which contains a history
substitution is printed before it is executed. A history substitution may
have an (see which indicates the event from which words are to be taken, a
(see which selects particular words from the chosen event, and/or a (see
which manipulates the selected words. A history event specification may be
one of (with the history substitution character shown): A number, referring
to a particular event. An offset, referring to the event before the
current event. The current event. This should be used carefully in where
there is no check for recursion. allows 10 levels of recursion. (+) The
previous event, equivalent to The most recent event whose first word begins
with the string The most recent event which contains the string The second
can be omitted if it is immediately followed by a newline. For example,
consider this bit of someone's history list:
9 8:30 nroff -man wumpus.man 10 8:31 cp wumpus.man wumpus.man.old
11 8:36 vi wumpus.man 12 8:37 diff wumpus.man.old wumpus.man The
commands are shown with their event numbers and time stamps. The current
event, which we haven't typed in yet, is event 13. Typing or refers to
event 11. Typing refers to the previous event, 12. can be abbreviated if
it is followed by which is described in and Typing refers to event 9, which
begins with Typing refers to event 12, which contains Without word
designators or modifiers history references simply expand to the entire
event, so we might type to redo the command (event 10) or if the output in
the previous event, 12, scrolled off the top of the screen. History
references may be insulated from the surrounding text with braces and if
necessary. For example, would look for a command beginning with and, in
this example, not find one, but would expand unambiguously to by matching
event 11. Even in braces, history substitutions do not nest. (+) While
expands, for example, to event 3 with the letter appended to it, expands it
to the last event beginning with only completely numeric arguments are
treated as event numbers. This makes it possible to recall events
beginning with numbers. To expand as in type To select words from an event
we can follow the event specification by a and a designator for the desired
words. The words of an input line are numbered from 0, the first (usually
command) word being 0, the second word (first argument) being 1, etc. The
basic word designators are, with columns for a leading and a leading (for
the abbreviated word designators - see The first (command) word. The th
argument. The first argument, equivalent to The last argument. The word
matched by an search. A range of words. Equivalent to Equivalent to but
returns nothing if the event contains only 1 word. Equivalent to
Equivalent to but omitting the last word Equivalent to the command and all
arguments except the last argument. Selected words are inserted into the
command line separated by single blanks. For example, the command (event
12) in the history list example in might have been typed as (using to
select the first argument from the previous event) or to select and swap
the arguments from the command (event 10). If we didn't care about the
order of the we might have typed or simply The command (event 10) might
have been typed using to refer to the current event. Typing would reuse
the first two words from the command (event 9) to expand to The separating
the event specification from the word designator can be omitted if the
argument selector begins with a or For example, our command (event 12)
might have been typed or, equivalently, However, if is abbreviated an
argument selector beginning with will be interpreted as an event
specification. A history reference may have a word designator but no event
specification. It then references the previous command. Continuing our
command example (event 12), we could have typed simply or, to get the
arguments in the opposite order, just The word or words in a history
reference can be edited, or by following it with one or more modifiers
(with the leading shown), each preceded by a Remove a trailing pathname
component, leaving the head. Remove all leading pathname components,
leaving the tail. Remove a filename extension leaving the root name.
Remove all but the extension. Uppercase the first lowercase letter.
Lowercase the first uppercase letter. Substitute for is simply a string
like not a regular expression as in the eponymous command. Any character
may be used as the delimiter in place of a can be used to quote the
delimiter inside and The character in the is replaced by also quotes If is
empty the from a previous substitution or the from a previous search or
event number in event specification is used. The trailing delimiter may be
omitted if it is immediately followed by a newline. Repeat the previous
substitution. Apply the following modifier once to each word. Apply the
following modifier as many times as possible to a single word. and can be
used together to apply a modifier globally. With the modifier, only the
patterns contained in the original word are substituted, not patterns that
contain any substitution result. Print the new command line but do not
execute it. Quote the substituted words, preventing further substitutions.
Same as but in addition preserve empty variables as a string containing a
NUL. This is useful to preserve positional arguments for example: > set
args=('arg 1' '' 'arg 3') > tcsh -f -c 'echo ${#argv}' $args:gQ 3 Like but
break into words at blanks, tabs and newlines. Modifiers are applied to
only the first modifiable word (unless is used). It is an error for no
word to be modifiable. For example, the command (event 12) in the history
list example in might have been typed as using to remove from the first
argument on the same line We could type then to capitalize to upper case
the first word to or to upper case all words. We might follow with to
correct the spelling of (see and for different approaches). (+) In as
such, only one modifier may be applied to each history or variable
expansion. In more than one may be used, for example % mv wumpus.man
/usr/share/man/man1/wumpus.1 % man !$:t:r man wumpus In the result would be
A substitution followed by a may need to be insulated from it with braces:
> mv a.out /usr/games/wumpus > setenv PATH !$:h:$PATH Bad ! modifier: $. >
setenv PATH !{-2$:h}:$PATH setenv PATH /usr/games:/bin:/usr/bin:. The
first attempt would succeed in but fails in because expects another
modifier after the second rather than There is a special abbreviation for
substitutions; when it is the first character on an input line, is
equivalent to Thus, we might follow the example from with to make the
spelling correction. This is the only history substitution which does not
explicitly begin with Finally, history can be accessed through the editor
as well as through the substitutions just described. The and and and and
and editor commands search for events in the history list and copy them
into the input buffer. The editor command switches between the expanded
and literal forms of history lines in the input buffer. and expand history
substitutions in the current word and in the entire input buffer
respectively. The shell maintains a list of aliases which can be set,
unset and printed by the and commands. After a command line is parsed into
simple commands (see the first word of each command, left-to-right, is
checked to see if it has an alias. If so, the first word is replaced by
the alias. If the alias contains a history reference, it undergoes as
though the original command were the previous input line. If the alias
does not contain a history reference, the argument list is left untouched.
Thus if the alias for were the command would become the argument list here
being undisturbed. If the alias for were then would become Aliases can be
used to introduce parser metasyntax. For example, defines a which its
arguments to the line printer. Alias substitution is repeated until the
first word of the command has no alias. If an alias substitution does not
change the first word (as in the previous example) it is flagged to prevent
a loop. Other loops are detected and cause an error. Some aliases are
referred to by the shell; see The shell maintains a list of variables, each
of which has as value a list of zero or more words. The values of shell
variables can be displayed and changed with the and commands. The system
maintains its own list of variables. These can be displayed and changed
with and (+) Variables may be made read-only with Read-only variables may
not be modified or unset; attempting to do so will cause an error. Once
made read-only, a variable cannot be made writable, so should be used with
caution. Environment variables cannot be made read-only. Some variables
are set by the shell or referred to by it. For instance, the variable is
an image of the shell's argument list, and words of this variable's value
are referred to in special ways. Some of the variables referred to by the
shell are toggles; the shell does not care what their value is, only
whether they are set or not. For instance, the variable is a toggle which
causes command input to be echoed. The command line option sets this
variable. lists all variables which are referred to by the shell. Other
operations treat variables numerically. The command permits numeric
calculations to be performed and the result assigned to a variable.
Variable values are, however, always represented as (zero or more) strings.
For the purposes of numeric operations, the null string is considered to be
zero, and the second and subsequent words of multi-word values are ignored.
After the input line is aliased and parsed, and before each command is
executed, variable substitution is performed keyed by characters. This
expansion can be prevented by preceding the with a except within pairs
where it occurs, and within pairs where it occurs. Strings quoted by are
interpreted later (see so substitution does not occur there until later, if
at all. A is passed unchanged if followed by a blank, tab, or end-of-line.
Input/output redirections are recognized before variable expansion, and are
variable expanded separately. Otherwise, the command name and entire
argument list are expanded together. It is thus possible for the first
(command) word (to this point) to generate more than one word, the first of
which becomes the command name, and the rest of which become arguments.
Unless enclosed in or given the modifier the results of variable
substitution may eventually be command and filename substituted. Within a
variable whose value consists of multiple words expands to a (portion of a)
single word, with the words of the variable's value separated by blanks.
When the modifier is applied to a substitution the variable will expand to
multiple words with each word separated by a blank and quoted to prevent
later command or filename substitution. The editor command normally bound
to can be used to interactively expand individual variables. The following
metasequences are provided for introducing variable values into the shell
input: Substitutes the words of the value of variable each separated by a
blank. Braces insulate from following characters which would otherwise be
part of it. Shell variables have names consisting of letters and digits
starting with a letter. The underscore character is considered a letter.
If is not a shell variable, but is set in the environment, then that value
is returned (but some of the other forms given below are not available in
this case). Substitutes only the selected words from the value of The is
subjected to substitution and may consist of a single number or two numbers
separated by a The first word of a variable's value is numbered If the
first number of a range is omitted it defaults to If the last member of a
range is omitted it defaults to The selects all words. It is not an error
for a range to be empty if the second argument is omitted or in range.
Substitutes the name of the file from which command input is being read.
An error occurs if the name is not known. Equivalent to Equivalent to
which is equivalent to Except as noted, it is an error to reference a
variable which is not set. The modifiers described under except for can be
applied to the substitutions above. More than one may be used. (+) Braces
may be needed to insulate a variable substitution from a literal just as
with any modifiers must appear within the braces. The following
substitutions cannot be modified with modifiers: Substitutes the string if
is set, if it is not. Substitutes if the current input filename is known,
if it is not. Always in interactive shells. Substitutes the number of
words in Equivalent to (+) Substitutes the number of characters in (+)
Substitutes the number of characters in (+) Equivalent to (+) Substitutes
the (decimal) process number of the (parent) shell. Substitutes the
(decimal) process number of the last background process started by this
shell. (+) Substitutes the command line of the last command executed. (+)
Substitutes a line from the standard input, with no further interpretation
thereafter. It can be used to read from the keyboard in a shell script.
(+) While always quotes as if it were equivalent to does not. Furthermore,
when is waiting for a line to be typed the user may type an interrupt to
interrupt the sequence into which the line is to be substituted, but does
not allow this. Substitutes the number of available bytes from the
standard input. (This feature might be non-portable.) (+) The remaining
substitutions are applied selectively to the arguments of builtin commands.
This means that portions of expressions which are not evaluated are not
subjected to these expansions. For commands which are not internal to the
shell, the command name is substituted separately from the argument list.
This occurs very late, after input-output redirection is performed, and in
a child of the main shell. Command substitution is indicated by a command
enclosed in The output from such a command is broken into separate words at
blanks, tabs and newlines, and null words are discarded. The output is
variable and command substituted and put in place of the original string.
Command substitutions inside double quotes retain blanks and tabs; only
newlines force new words. The single final newline does not force a new
word in any case. It is thus possible for a command substitution to yield
only part of a word, even if the command outputs a complete line. By
default, the shell since version 6.12 replaces all newline and carriage
return characters in the command by spaces. If this is switched off by
unsetting newlines separate commands as usual. If a word contains any of
the characters or or begins with the character it is a candidate for
filename substitution, also known as This word is then regarded as a
pattern and replaced with an alphabetically sorted list of file names which
match the pattern. In matching filenames, the character at the beginning
of a filename or immediately following a as well as the character must be
matched explicitly (unless either or or both are set (+)). The character
matches any string of characters, including the null string. The character
matches any single character. The sequence matches any one of the
characters enclosed. Within a pair of characters separated by matches any
character lexically between the two. (+) Some glob-patterns can be
negated: The sequence matches any single character specified by the
characters and/or ranges of characters in the braces. An entire glob-
pattern can also be negated with > echo * bang crash crunch ouch > echo
^cr* bang ouch Glob-patterns which do not use or or which use or (below)
are not negated correctly. The metanotation is a shorthand for Left-to-
right order is preserved: expands to The results of matches are sorted
separately at a low level to preserve this order: might expand to (Note
that was not sorted with the results of matching It is not an error when
this construct expands to files which do not exist, but it is possible to
get an error from a command to which the expanded list is passed. This
construct may be nested. As a special case the words and are passed
undisturbed. The character at the beginning of a filename refers to home
directories. Standing alone, i.e., it expands to the invoker's home
directory as reflected in the value of the shell variable. When followed
by a name consisting of letters, digits and characters the shell searches
for a user with that name and substitutes their home directory; thus might
expand to and might expand to If the character is followed by a character
other than a letter or or appears elsewhere than at the beginning of a
word, it is left undisturbed. A command like does not, therefore, do home
directory substitution as one might hope. It is an error for a glob-
pattern containing or with or without not to match any files. However,
only one pattern in a list of glob-patterns must match a file (so that,
e.g., would fail only if there were no files in the current directory
ending in or and if the shell variable is set a pattern (or list of
patterns) which matches nothing is left unchanged rather than causing an
error. The shell variable can be set to allow or as a file glob pattern
that matches any string of characters including recursively traversing any
existing sub-directories. For example, will list all the .c files in the
current directory tree. If used by itself, it will match zero or more
sub-directories. For example will list any file named in the directory
tree; will match any file in the directory tree ending in and will match
any .h file with either in a subdirectory name or in the filename itself.
To prevent problems with recursion, the glob-pattern will not descend into
a symbolic link containing a directory. To override this, use (+) The
shell variable can be set to prevent filename substitution, and the editor
command, normally bound to can be used to interactively expand individual
filename substitutions. The directory stack is a list of directories,
numbered from zero, used by the and builtin commands. can print, store in
a file, restore and clear the directory stack at any time, and the and
shell variables can be set to store the directory stack automatically on
logout and restore it on login. The shell variable can be examined to see
the directory stack and set to put arbitrary directories into the directory
stack. The character followed by one or more digits expands to an entry in
the directory stack. The special case expands to the last directory in the
stack. For example, > dirs -v 0 /usr/bin 1 /usr/spool/uucp 2
/usr/accts/sys > echo =1 /usr/spool/uucp > echo =0/calendar
/usr/bin/calendar > echo =- /usr/accts/sys The and shell variables and the
editor command apply to directory stack as well as filename substitutions.
There are several more transformations involving filenames, not strictly
related to the above but mentioned here for completeness. filename may be
expanded to a full path when the variable is set to Quoting prevents this
expansion, and the editor command does it on demand. The editor command
expands commands in into full paths on demand. Finally, and interpret as
the old working directory (equivalent to the shell variable This is not a
substitution at all, but an abbreviation recognized by only those commands.
Nonetheless, it too can be prevented by quoting. The next three sections
describe how the shell executes commands and deals with their input and
output. A simple command is a sequence of words, the first of which
specifies the command to be executed. A series of simple commands joined
by characters forms a pipeline. The output of each command in a pipeline
is connected to the input of the next. Simple commands and pipelines may
be joined into sequences with and will be executed sequentially. Commands
and pipelines can also be joined into sequences with or indicating, as in
the C language, that the second is to be executed only if the first fails
or succeeds respectively. A simple command, pipeline or sequence may be
placed in parentheses and to form a simple command, which may in turn be a
component of a pipeline or sequence. A command, pipeline or sequence can
be executed without waiting for it to terminate by following it with an
Builtin commands are executed within the shell. If any component of a
pipeline except the last is a builtin command, the pipeline is executed in
a subshell. Parenthesized commands are always executed in a subshell.
(cd; pwd); pwd thus prints the directory, leaving you where you were
(printing this after the home directory), while cd; pwd leaves you in the
directory. Parenthesized commands are most often used to prevent from
affecting the current shell. When a command to be executed is found not to
be a builtin command the shell attempts to execute the command via Each
word in the variable names a directory in which the shell will look for the
command. If the shell is not given a option, the shell hashes the names in
these directories into an internal table so that it will try an in only a
directory where there is a possibility that the command resides there.
This greatly speeds command location when a large number of directories are
present in the search path. This hashing mechanism is not used: If hashing
is turned explicitly off via If the shell was given a For each directory
component of which does not begin with a If the command contains a In the
above four cases the shell concatenates each component of the path vector
with the given command name to form a path name of a file which it then
attempts to execute it. If execution is successful, the search stops. If
the file has execute permissions but is not an executable to the system
(i.e., it is neither an executable binary nor a script that specifies its
interpreter), then it is assumed to be a file containing shell commands and
a new shell is spawned to read it. The special alias may be set to specify
an interpreter other than the shell itself. On systems which do not
understand the script interpreter convention the shell may be compiled to
emulate it; see the shell variable. If so, the shell checks the first line
of the file to see if it is of the form If it is, the shell starts with the
given s and feeds the file to it on standard input. The standard input and
standard output of a command may be redirected with the following syntax:
Open file (which is first variable, command and filename expanded) as the
standard input. Read the shell input up to a line which is identical to is
not subjected to variable, filename or command substitution, and each input
line is compared to before any substitutions are done on this input line.
Unless a quoting or appears in variable and command substitution is
performed on the intervening lines, allowing to quote and Commands which
are substituted have all blanks, tabs, and newlines preserved, except for
the final newline which is dropped. The resultant text is placed in an
anonymous temporary file which is given to the command as standard input.
The file is used as standard output. If the file does not exist then it is
created; if the file exists, it is truncated, its previous contents being
lost. If the shell variable is set, then the file must not exist or be a
character special file (e.g., a terminal or or an error results. This
helps prevent accidental destruction of files. In this case the forms can
be used to suppress this check. If is given in is allowed on empty files;
if is given in an interactive confirmation is presented, rather than an
error. The forms involving route the diagnostic output into the specified
file as well as the standard output. is expanded in the same way as input
filenames are. Like but appends output to the end of If the shell variable
is set, then it is an error for the file to exist, unless one of the forms
is given. A command receives the environment in which the shell was
invoked as modified by the input-output parameters and the presence of the
command in a pipeline. Thus, unlike some previous shells, commands run
from a file of shell commands have no access to the text of the commands by
default; rather they receive the original standard input of the shell. The
mechanism should be used to present inline data. This permits shell
command scripts to function as components of pipelines and allows the shell
to block read its input. Note that the default standard input for a
command run detached is the empty file but the original standard input of
the shell. If this is a terminal and if the process attempts to read from
the terminal, then the process will block and the user will be notified
(see Diagnostic output may be directed through a pipe with the standard
output. Simply use the form rather than just The shell cannot presently
redirect diagnostic output without also redirecting standard output, but is
often an acceptable workaround. Either or may be to send output to the
terminal. Having described how the shell accepts, parses and executes
command lines, we now turn to a variety of its useful features. The shell
contains a number of commands which can be used to regulate the flow of
control in command files (shell scripts) and (in limited but useful ways)
from terminal input. These commands all operate by forcing the shell to
reread or skip in its input and, due to the implementation, restrict the
placement of some of the commands. The and statements, as well as the form
of the statement, require that the major keywords appear in a single simple
command on an input line as shown below. If the shell's input is not
seekable, the shell buffers up input whenever a loop is being read and
performs seeks in this internal buffer to accomplish the rereading implied
by the loop. (To the extent that this allows, backward s will succeed on
non-seekable inputs.) The and builtin commands use expressions with a
common syntax. The expressions can include any of the operators described
in the next three sections. Note that the builtin command has its own
separate syntax. These operators are similar to those of C and have the
same precedence. The operators, in descending precedence, with equivalent
precedence per line, are: The and operators compare their arguments as
strings; all others operate on numbers. The operators and are like and
except that the right hand side is a glob-pattern (see against which the
left hand operand is matched. This reduces the need for use of the builtin
command in shell scripts when all that is really needed is pattern
matching. Null or missing arguments are considered The results of all
expressions are strings, which represent decimal numbers. It is important
to note that no two components of an expression can appear in the same
word; except when adjacent to components of expressions which are
syntactically significant to the parser they should be surrounded by
spaces. Commands can be executed in expressions and their exit status
returned by enclosing them in braces and Remember that the braces should be
separated from the words of the command by spaces. Command executions
succeed, returning true, i.e., if the command exits with status 0,
otherwise they fail, returning false, i.e., If more detailed status
information is required then the command should be executed outside of an
expression and the shell variable examined. Some of these operators
perform true/false tests on files and related objects. They are of the
form where is one of: Read access. Write access. Execute access.
Executable in the path or shell builtin, e.g., and are generally true, but
is not. (+) Existence. Ownership. Zero size. Non-zero size. (+) Plain
file. Directory. Symbolic link. (+) * Block special file. (+) Character
special file. (+) Named pipe (fifo). (+) * Socket special file. (+) * Set-
user-ID bit is set. (+) Set-group-ID bit is set. (+) Sticky bit is set. (+)
(which must be a digit) is an open file descriptor for a terminal device.
(+) Has been migrated (Convex only). (+) Applies subsequent operators in a
multiple-operator test to a symbolic link rather than to the file to which
the link points. (+) * is command and filename expanded and then tested to
see if it has the specified relationship to the real user. If does not
exist or is inaccessible or, for the operators indicated by if the
specified file type does not exist on the current system, then all
inquiries return false, i.e., These operators may be combined for
conciseness: is equivalent to (+) For example, is true (returns for plain
executable files, but not for directories. may be used in a multiple-
operator test to apply subsequent operators to a symbolic link rather than
to the file to which the link points. For example, is true for links owned
by the invoking user. and are always true for links and false for non-
links. has a different meaning when it is the last operator in a
multiple-operator test; see below. It is possible but not useful, and
sometimes misleading, to combine operators which expect to be a file with
operators which do not (e.g., and Following with a non-file operator can
lead to particularly strange results. Other operators return other
information, i.e., not just or (+) They have the same format as before; may
be one of: Last file access time, as the number of seconds since the epoch.
Like but in timestamp format, e.g., Last file modification time. Like but
in timestamp format. Last inode modification time. Like but in timestamp
format. Device number. Inode number. Composite ile identifier, in the
form The name of the file pointed to by a symbolic link. Number of (hard)
links. Permissions, in octal, without leading zero. Like with leading
zero. Equivalent to For example, returns if is writable by group and
other, if by group only, and if by neither. Like with leading zero.
Numeric userid. Username, or the numeric userid if the username is
unknown. Numeric groupid. Groupname, or the numeric groupid if the
groupname is unknown. Size, in bytes. Only one of these operators may
appear in a multiple-operator test, and it must be the last. Note that has
a different meaning at the end of and elsewhere in a multiple-operator
test. Because is a valid return value for many of these operators, they do
not return when they fail: most return and returns If the shell is compiled
with POSIX defined (see the shell variable), the result of a file inquiry
is based on the permission bits of the file and not on the result of the
system call. For example, if one tests a file with whose permissions would
ordinarily allow writing but which is on a file system mounted read-only,
the test will succeed in a POSIX shell but fail in a non-POSIX shell. File
inquiry operators can also be evaluated with the builtin command (+). The
shell associates a with each pipeline. It keeps a table of current jobs,
printed by the command, and assigns them small integer numbers. When a job
is started asynchronously with the shell prints a line which looks like [1]
1234 indicating that the job which was started asynchronously was job
number 1 and had one (top-level) process, whose process id was 1234. If
you are running a job and wish to do something else you may hit the suspend
key (usually which sends a STOP signal to the current job. The shell will
then normally indicate that the job has been and print another prompt. If
the shell variable is set, all jobs will be listed like the builtin
command; if it is set to the listing will be in long format, like You can
then manipulate the state of the suspended job. You can put it in the with
the command or run some other commands and eventually bring the job back
into the with (See also the editor command.) A takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed. The builtin command causes the shell to wait for all
background jobs to complete. The key sends a delayed suspend signal, which
does not generate a STOP signal until a program attempts to it, to the
current job. This can usefully be typed ahead when you have prepared some
commands for a job which you wish to stop after it has read them. The key
performs this function in in is an editing command. (+) A job being run in
the background stops if it tries to read from the terminal. Background
jobs are normally allowed to produce output, but this can be disabled by
giving the command If you set this tty option, then background jobs will
stop when they try to produce output like they do when they try to read
input. There are several ways to refer to jobs in the shell. The
character introduces a job name. If you wish to refer to job number 1, you
can name it as Just naming a job brings it to the foreground; thus is a
synonym for bringing job 1 back into the foreground. Similarly, typing
resumes job 1 in the background, just like A job can also be named by an
unambiguous prefix of the string typed in to start it: would normally
restart a suspended job, if there were only one suspended job whose name
began with the string It is also possible to type to specify a job whose
text contains if there is only one such job. The shell maintains a notion
of the current and previous jobs. In output pertaining to jobs, the
current job is marked with a and the previous job with a The abbreviations
and (by analogy with the syntax of the mechanism) all refer to the current
job, and refers to the previous job. The job control mechanism requires
that the option be set on some systems. It is an artifact from a
implementation of the tty driver which allows generation of interrupt
characters from the keyboard to tell jobs to stop. See and the builtin
command for details on setting options in the new tty driver. The shell
learns immediately whenever a process changes state. It normally informs
you whenever a job becomes blocked so that no further progress is possible,
but only right before it prints a prompt. This is done so that it does not
otherwise disturb your work. If, however, you set the shell variable the
shell will notify you immediately of changes of status in background jobs.
There is also a builtin command which marks a single process so that its
status changes will be immediately reported. By default marks the current
process; simply enter after starting a background job to mark it for
immediate status reporting. When you try to leave the shell while jobs are
stopped, you will be warned that You may use the command to see what they
are. If you do this or immediately try to exit again, the shell will not
warn you a second time, and the suspended jobs will be terminated. There
are various ways to run commands and take other actions automatically at
various times in the of the shell. They are summarized here, and described
in detail under the appropriate and The builtin command puts commands in a
scheduled-event list, to be executed by the shell at a given time. The and
can be set, respectively, to execute commands: when the shell wants to ring
the bell, when the working directory changes, when a job is started or is
brought into the foreground, every minutes, before each prompt, and before
each command gets executed. The shell variable can be set to log out or
lock the shell after a given number of minutes of inactivity. The shell
variable can be set to check for new mail periodically. The shell variable
can be set to print the exit status of commands which exit with a status
other than zero. The shell variable can be set to ask the user, when is
typed, if that is really what was meant. The shell variable can be set to
execute the builtin command after the completion of any process that takes
more than a given number of CPU seconds. The and shell variables can be
set to report when selected users log in or out, and the builtin command
reports on those users at any time. The shell is eight bit clean (if so
compiled; see the shell variable) and thus supports character sets needing
this capability. NLS support differs depending on whether or not the shell
was compiled to use the system's NLS (again, see In either case, 7-bit
ASCII is the default character code (e.g., the classification of which
characters are printable) and sorting, and changing the or environment
variables causes a check for possible changes in these respects. When
using the system's NLS, the function is called to determine appropriate
character code/classification and sorting (e.g., would yield as the
character code). This function typically examines the and environment
variables; refer to the system documentation for further details. When not
using the system's NLS, the shell simulates it by assuming that the ISO
8859-1 character set is used whenever either of the and variables are set,
regardless of their values. Sorting is not affected for the simulated NLS.
In addition, with both real and simulated NLS, all printable characters in
the range \200-\377, i.e., those that have bindings, are automatically
rebound to The corresponding binding for the sequence, if any, is left
alone. These characters are not rebound if the environment variable is
set. This may be useful for the simulated NLS or a primitive real NLS
which assumes full ISO 8859-1. Otherwise, all bindings in the range
\240-\377 are effectively undone. Explicitly rebinding the relevant keys
with is of course still possible. Unknown characters (i.e., those that are
neither printable nor control characters) are printed in the format \nnn.
If the tty is not in 8 bit mode, other 8 bit characters are printed by
converting them to ASCII and using standout mode. The shell never changes
the 7/8 bit mode of the tty and tracks user-initiated changes of 7/8 bit
mode. NLS users (or, for that matter, those who want to use a meta key)
may need to explicitly set the tty in 8 bit mode through the appropriate
command in, e.g., the file. A number of new builtin commands are provided
to support features in particular operating systems. All are described in
detail in the section. On systems that support TCF (aix-ibm370, aix-ps2),
and get and set the system execution path, and get and set the experimental
version prefix and migrates processes between sites. The builtin prints
the site on which each job is executing. Under BS2000, executes commands
of the underlying BS2000/OSD operating system. Under Domain/OS, adds
shared libraries to the current environment, changes the rootnode and
changes the systype. Under Mach, is equivalent to Mach's Under
Masscomp/RTU and Harris CX/UX, sets the universe. Under Harris CX/UX, or
runs a command under the specified universe. Under Convex/OS, prints or
sets the universe. The and environment variables indicate respectively the
vendor, operating system and machine type (microprocessor class or machine
model) of the system on which the shell thinks it is running. These are
particularly useful when sharing one's home directory between several types
of machines; one can, for example, set path = (~/bin.$MACHTYPE /usr/ucb
/bin /usr/bin .) in one's and put executables compiled for each machine in
the appropriate directory. The shell variable indicates what options were
chosen when the shell was compiled. Note also the builtin, the and shell
variables and the system-dependent locations of the shell's input files
(see Login shells ignore interrupts when reading the file The shell ignores
quit signals unless started with Login shells catch the terminate signal,
but non-login shells inherit the terminate behavior from their parents.
Other signals have the values which the shell inherited from its parent.
In shell scripts, the shell's handling of interrupt and terminate signals
can be controlled with and its handling of hangups can be controlled with
and The shell exits on a hangup (see also the shell variable). By default,
the shell's children do too, but the shell does not send them a hangup when
it exits. arranges for the shell to send a hangup to a child when it
exits, and sets a child to ignore hangups. The shell uses three different
sets of terminal modes: used when editing; used when quoting literal
characters; and used when executing commands. The shell holds some
settings in each mode constant, so commands which leave the tty in a
confused state do not interfere with the shell. The shell also matches
changes in the speed and padding of the tty. The list of tty modes that
are kept constant can be examined and modified with the builtin. Note that
although the editor uses CBREAK mode (or its equivalent), it takes typed-
ahead characters anyway. The and commands can be used to manipulate and
debug terminal capabilities from the command line. On systems that support
SIGWINCH or SIGWINDOW, the shell adapts to window resizing automatically
and adjusts the environment variables and if set. If the environment
variable contains and fields, the shell adjusts them to reflect the new
window size. The next sections of this manual describe all of the
available and A synonym for the builtin command. A synonym for the builtin
command. Does nothing, successfully. The first form prints the values of
all shell variables. The second form assigns the value of to The third
form assigns the value of to the 'th component of both and its 'th
component must already exist. may contain the operators etc., as in C. If
contains or then at least that part of must be placed within and Note that
the syntax of has nothing to do with that described under The fourth and
fifth forms increment or decrement or its 'th component. The space between
and is required. The spaces between and and between and are optional.
Components of must be separated by spaces. Without arguments, prints all
aliases. With prints the alias for name. With and assigns as the alias of
is command and filename substituted. may not be or See also the builtin
command. Shows the amount of dynamic memory acquired, broken down into
used and free memory. With an argument shows the number of free and used
blocks in each size category. The categories start at size 8 and double at
each step. This command's output may vary across system types, because
systems other than the VAX may use a different memory allocator. Puts the
specified jobs (or, without arguments, the current job) into the
background, continuing each if it is stopped. may be a number, a string,
or as described under The first form either lists all bound keys and the
editor command to which each is bound, lists a description of the commands,
or binds all keys to a specific mode. The second form lists the editor
command to which is bound. The third form binds the editor command to
Supported options: Lists or changes key-bindings in the alternative key
map. This is the key map used in command mode. is interpreted as a
control character written (e.g., or (e.g., a meta character written (e.g.,
a function key written (e.g., or an extended prefix key written (e.g., is
interpreted as a builtin or external command instead of an editor command.
Binds all keys to the standard bindings for the default editor, as per and
Binds all keys to -style bindings. Unsets is interpreted as a symbolic
arrow key name, which may be one of or Lists all editor commands and a
short description of each. Removes 's binding. Be careful: does bind to
it unbinds completely. is taken as a literal string and treated as
terminal input when is typed. Bound keys in are themselves reinterpreted,
and this continues for ten levels of interpretation. Prints a usage
message. Binds all keys to -style bindings. Sets Forces a break from
option processing, so the next word is taken as even if it begins with may
be a single character or a string. If a command is bound to a string, the
first character of the string is bound to and the entire string is bound to
the command. Control characters in can be literal (they can be typed by
preceding them with the editor command normally bound to or written caret-
character style, e.g., Delete is written (caret-question mark). and can
contain backslashed escape sequences (in the style of System V as follows:
Bell. Backspace. Escape. Form feed. Newline. Carriage return.
Horizontal tab. Vertical tab. The ASCII character corresponding to the
octal number nullifies the special meaning of the following character, if
it has any, notably and Passes to the BS2000 command interpreter for
execution. Only non-interactive commands can be executed, and it is not
possible to execute any command that would overlay the image of the current
process, like /EXECUTE or /CALL-PROCEDURE. (BS2000 only) Causes execution
to resume after the of the nearest enclosing or The remaining commands on
the current line are executed. Multi-level breaks are thus possible by
writing them all on one line. Causes a break from a resuming after the
Prints the names of all builtin commands. A synonym for the builtin
command. Available only if the shell was so compiled; see the shell
variable. A label in a statement as discussed below. If a directory is
given, changes the shell's working directory to If not, changes to unless
the variable is not set, in which case a is required. If is it is
interpreted as the previous working directory (see (+) If is not a
subdirectory of the current directory (and does not begin with or each
component of the variable is checked to see if it has a subdirectory
Finally, if all else fails but is a shell variable whose value begins with
or then this is tried to see if it is a directory, and the option is
implied. With prints the final directory stack, just like The and flags
have the same effect on as on and they imply (+). Using forces a break
from option processing so the next word is taken as the directory even if
it begins with (+). See also the and shell variables. A synonym for the
builtin command. ... (+) Without arguments, lists all completions. With
lists completions for With and ..., defines completions. may be a full
command name or a glob-pattern (see It can begin with to indicate that
completion should be used only when is ambiguous. specifies which word
relative to the current word is to be completed, and may be one of the
following: Current-word completion. is a glob-pattern which must match the
beginning of the current word on the command line. is ignored when
completing the current word. Like but includes when completing the current
word. Next-word completion. is a glob-pattern which must match the
beginning of the previous word on the command line. Like but must match
the beginning of the word two before the current word. Position-dependent
completion. is a numeric range, with the same syntax used to index shell
variables, which must include the current word. the list of possible
completions, may be one of the following: Aliases. Bindings (editor
commands). Commands (builtin or external commands). External commands
which begin with the supplied path prefix. Directories. Directories which
begin with the supplied path prefix. Environment variables. Filenames.
Filenames which begin with the supplied path prefix. Groupnames. Jobs.
Limits. Nothing. Shell variables. Signals. Plain files. Plain files
which begin with the supplied path prefix. Any variables. Usernames.
Like but prints when is used. Completions. Words from the variable Words
from the given list. Words from the output of command. is an optional
glob-pattern. If given, words from only that match are considered and the
shell variable is ignored. The types and may not have a pattern, and uses
as an explanatory message when the editor command is used. is a single
character to be appended to a successful completion. If null, no character
is appended. If omitted (in which case the fourth delimiter can also be
omitted), a slash is appended to directories and a space to other words.
invoked from has the additional environment variable set, which contains
(as its name indicates) contents of the current (already typed in) command
line. One can examine and use contents of the environment variable in a
custom script to build more sophisticated completions (see completion for
included in this package). Now for some examples. Some commands take only
directories as arguments, so there's no point completing plain files. >
complete cd 'p/1/d/' completes only the first word following with a
directory. -type completion can also be used to narrow down command
completion: > co[^D] complete compress > complete -co* 'p/0/(compress)/' >
co[^D] > compress This completion completes commands (words in position 0,
which begin with (thus matching to (the only word in the list). The
leading indicates that this completion is to be used with only ambiguous
commands. > complete find 'n/-user/u/' is an example of -type completion.
Any word following and immediately following is completed from the list of
users. > complete cc 'c/-I/d/' demonstrates -type completion. Any word
following and beginning with is completed as a directory. is not taken as
part of the directory because we used lowercase Different are useful with
different commands. > complete alias 'p/1/a/' > complete man 'p/*/c/' >
complete set 'p/1/s/' > complete true 'p/1/x:Truth has no options./' These
complete words following with aliases, with commands, and with shell
variables. doesn't have any options, so does nothing when completion is
attempted and prints when completion choices are listed. Note that the
example, and several other examples below, could just as well have used or
as Words can be completed from a variable evaluated at completion time, >
complete ftp 'p/1/$hostnames/' > set hostnames = (rtfm.mit.edu
tesla.ee.cornell.edu) > ftp [^D] rtfm.mit.edu tesla.ee.cornell.edu > ftp
[^C] > set hostnames = (rtfm.mit.edu tesla.ee.cornell.edu uunet.uu.net) >
ftp [^D] rtfm.mit.edu tesla.ee.cornell.edu uunet.uu.net or from a command
run at completion time: > complete kill 'p/*/`ps | awk \{print\ \$1\}`/' >
kill -9 [^D] 23113 23377 23380 23406 23429 23529 23530 PID Note that the
command does not itself quote its arguments, so the braces, space and in
must be quoted explicitly. One command can have multiple completions: >
complete dbx 'p/2/(core)/' 'p/*/c/' completes the second argument to with
the word and all other arguments with commands. Note that the positional
completion is specified before the next-word completion. Because
completions are evaluated from left to right, if the next-word completion
were specified first it would always match and the positional completion
would never be executed. This is a common mistake when defining a
completion. The pattern is useful when a command takes files with only
particular forms as arguments. For example, > complete cc 'p/*/f:*.[cao]/'
completes arguments to files ending in only or can also exclude files,
using negation of a glob-pattern as described under One might use >
complete rm 'p/*/f:^*.{c,h,cc,C,tex,1,man,l,y}/' to exclude precious source
code from completion. Of course, one could still type excluded names
manually or override the completion mechanism using the or editor commands.
The and are like and respectively, but they use the argument in a different
way: to restrict completion to files beginning with a particular path
prefix. For example, the Elm mail program uses as an abbreviation for
one's mail directory. One might use > complete elm c@=@F:$HOME/Mail/@ to
complete as if it were Note that we used the separator instead of to avoid
confusion with the argument, and we used instead of because home directory
substitution works at only the beginning of a word. is used to add a
nonstandard suffix (not space or for directories) to completed words. >
complete finger 'c/*@/$hostnames/' 'p/1/u/@' completes arguments to from
the list of users, appends an and then completes after the from the
variable. Note again the order in which the completions are specified.
Finally, here's a complex example for inspiration: > complete find \
'n/-name/f/' 'n/-newer/f/' 'n/-{,n}cpio/f/' \ 'n/-exec/c/' 'n/-ok/c/'
'n/-user/u/' \ 'n/-group/g/' 'n/-fstype/(nfs 4.2)/' \ 'n/-type/(b c d f l p
s)/' \ 'c/-/(name newer cpio ncpio exec ok user \ group fstype type atime
ctime depth inum \ ls mtime nogroup nouser perm print prune \ size xdev)/'
\ 'p/*/d/' This completes words following or (note the pattern which
matches both) to files, words following or to commands, words following and
to users and groups respectively and words following or to members of the
given lists. It also completes the switches themselves from the given list
(note the use of -type completion) and completes anything not otherwise
completed to a directory. Whew. Remember that programmed completions are
ignored if the word being completed is a tilde substitution (beginning with
or a variable (beginning with See also the builtin command. Continues
execution of the nearest enclosing or The rest of the commands on the
current line are executed. Labels the default case in a statement. It
should come after all labels. (+) (+) The first form prints the directory
stack. The top of the stack is at the left and the first directory in the
stack is the current directory. With or in the output is expanded
explicitly to or the pathname of the home directory for user (+) With
entries are wrapped before they reach the edge of the screen. (+) With
entries are printed one per line, preceded by their stack positions. (+)
If more than one of or is given, takes precedence. is accepted but does
nothing. The second form with saves the directory stack to as a series of
and commands. The second form with sources which is presumably a directory
stack file saved by the option or the mechanism. In either case, is used
if is not given and is used if is unset. Note that login shells do the
equivalent of on startup and, if is set, before exiting. Because only is
normally sourced before should be set in rather than The third form clears
the directory stack. Writes each to the shell's standard output, separated
by spaces and terminated with a newline. The shell variable may be set to
emulate (or not) the flags and escape sequences of the BSD and/or System V
versions of see and Exercises the terminal capabilities (see in For
example, sends the cursor to the home position, sends it to column 3 and
row 10, and prints in the status line. If is or prints the value of that
capability or indicating that the terminal does or does not have that
capability). One might use this to make the output from a shell script
less verbose on slow terminals, or limit command output to the number of
lines on the screen: > set history=`echotc lines` > @ history-- Termcap
strings may contain wildcards which will not echo correctly. One should
use double quotes when setting a shell variable to a terminal capability
string, as in the following example that places the date in the status
line: > set tosl="`echotc ts 0`" > set frsl="`echotc fs`" > echo -n
"$tosl";date; echo -n "$frsl" With nonexistent capabilities return the
empty string rather than causing an error. With messages are verbose. See
the description of the and statements below. Treats the arguments as input
to the shell and executes the resulting command(s) in the context of the
current shell. This is usually used to execute commands generated as the
result of command or variable substitution, because parsing occurs before
these substitutions. See for a sample use of Executes the specified in
place of the current shell. The shell exits either with the value of the
specified (an expression, as described under or, without with the value 0.
Brings the specified jobs (or, without arguments, the current job) into the
foreground, continuing each if it is stopped. may be a number, a string,
or as described under See also the editor command. Applies (which is a
file inquiry operator as described under to each and returns the results as
a space-separated list. Successively sets the variable to each member of
and executes the sequence of commands between this command and the matching
(Both and must appear alone on separate lines.) The builtin command may be
used to continue the loop prematurely and the builtin command to terminate
it prematurely. When this command is read from the terminal, the loop is
read once prompting with (or before any statements in the loop are
executed. If you make a mistake typing in a loop at the terminal you can
rub it out. Prints the system execution path. (TCF only) Prints the
experimental version prefix. (TCF only) Like but the parameter is not
recognized and words are delimited by null characters in the output.
Useful for programs which wish to use the shell to filename expand a list
of words. is filename and command-substituted to yield a string of the
form The shell rewinds its input as much as possible, searches for a line
of the form possibly preceded by blanks or tabs, and continues execution
after that line. Prints a statistics line indicating how effective the
internal hash table has been at locating commands (and avoiding 's). An is
attempted for each component of the where the hash function indicates a
possible hit, and in each component which does not begin with a On machines
without prints only the number and size of hash buckets. (+) (+) The first
form prints the history event list. If is given only the most recent
events are printed or saved. With the history list is printed without
leading numbers. If is specified, timestamps are printed also in comment
form. This can be used to produce files suitable for loading with or With
the order of printing is most recent first rather than oldest first. The
second form with saves the history list to If the first word of the shell
variable is set to a number, at most that many lines are saved. If the
second word of is set to the history list is merged with the existing
history file instead of replacing it (if there is one) and sorted by time
stamp. (+) Merging is intended for an environment like the X Window System
with several shells in simultaneous use. If the second word of is and the
third word is set to the history file update will be serialized with other
shell sessions that would possibly like to merge history at exactly the
same time. The second form with appends (which is presumably a history
list saved by the option or the mechanism) to the history list. is like
but the contents of are merged into the history list and sorted by
timestamp. In either case, is used if is not given and is used if is
unset. Note that is exactly like except that it does not require a
filename. Note that login shells do the equivalent of on startup and, if
is set, before exiting. Because only is normally sourced before should be
set in rather than If is set, the first and second forms print and save the
literal (unexpanded) form of the history list. The third form clears the
history list. With runs such that it will exit on a hangup signal and
arranges for the shell to send it a hangup signal when the shell exits.
Note that commands may set their own response to hangups, overriding
Without an argument, causes the non-interactive shell only to exit on a
hangup for the remainder of the script. See also and the builtin command.
If (an expression, as described under evaluates true, then is executed.
Variable substitution on happens early, at the same time it does for the
rest of the command. must be a simple command, not an alias, a pipeline, a
command list or a parenthesized command list, but it may have arguments.
Input/output redirection occurs even if is false and is thus executed; this
is a bug. If the specified is true then the commands to the first are
executed; otherwise if is true then the commands to the second are
executed, etc. Any number of pairs are possible; only one is needed. The
part is likewise optional. (The words and must appear at the beginning of
input lines; the must appear alone on its input line or after an Adds each
to the current environment. There is no way to remove a shared library.
(Domain/OS only) The first form lists the active jobs. With lists process
IDs in addition to the normal information. On TCF systems, prints the site
on which each job is executing. The second form with the option sets the
process title to using where available. If no is provided, the process
title will be cleared. The first form lists the signal names. The second
form sends the specified (or, if none is given, the TERM (terminate)
signal) to the specified jobs or processes. may be a number, a string, or
as described under Signals are either given by number or by name (as given
in stripped of the prefix There is no default entering just does not send a
signal to the current job. If the signal being sent is TERM (terminate) or
HUP (hangup), then the job or process is sent a CONT (continue) signal as
well. Limits the consumption by the current process and each process it
creates to not individually exceed on the specified If no is given, then
the current limit for is printed. If no is given, then all limitations are
given. If the flag is given, the hard limits are used instead of the
current limits. The hard limits impose a ceiling on the values of the
current limits. Only the super-user may raise the hard limits, but a user
may lower or raise the current limits within the legal range. Controllable
types currently include (if supported by the OS): Maximum number of threads
for this process. Size of the largest core dump that will be created.
Maximum number of cpu-seconds to be used by each process. Maximum growth
of the data+stack region via beyond the end of the program text. Maximum
number of open files for this process. Largest single file which can be
created. Maximum amount of memory a process may allocate per system call.
Maximum number of kqueues allocated for this process. Maximum number of
locks for this user. Maximum number of bytes in POSIX mqueues for this
user. Maximum nice priority the user is allowed to raise mapped from
[19...-20] to [0...39] for this user. Maximum number of simultaneous
processes for this user id. Maximum realtime priority for this user.
Timeout for RT tasks in microseconds for this user. Maximum number of
pending signals for this user. Maximum number of simultaneous threads
(lightweight processes) for this user id. Maximum size which a process may
lock into memory using Maximum amount of physical memory a process may have
allocated to it at a given time. Maximum number of POSIX advisory locks
for this user. Maximum number of pseudo-terminals for this user. Maximum
size of socket buffer usage for this user. Maximum size of the
automatically-extended stack region. Maximum amount of swap space reserved
or used for this user. Maximum number of threads for this process.
Maximum amount of virtual memory a process may have allocated to it at a
given time (address space). may be given as a (floating point or integer)
number followed by a scale factor. For all limits other than the default
scale is or (1024 bytes); a scale factor of or (1048576 bytes) or or
(1073741824 bytes) may also be used. For the default scaling is while for
minutes or for hours, or a time of the form giving minutes and seconds may
be used. If is then the limitation on the specified is removed (this is
equivalent to the builtin command). For both names and scale factors,
unambiguous prefixes of the names suffice. Prints the shell variable and
reports on each user indicated in who is logged in, regardless of when they
last logged in. See also Terminates a login shell, replacing it with an
instance of This is one way to log off, included for compatibility with
Terminates a login shell. Especially useful if is set. (+) Lists files
like but much faster. identifies each type of special file in the listing
with a special character suffix: Directory. Executable. Block device.
Character device. Named pipe (systems with named pipes only). Socket
(systems with sockets only). Symbolic link (systems with symbolic links
only). Hidden directory (AIX only) or context dependent (HP/UX only).
Network special (HP/UX only). If the shell variable is set, symbolic links
are identified in more detail (on only systems that have them, of course):
Symbolic link to a non-directory. Symbolic link to a directory. Orphaned
(broken) symbolic link. also slows down and causes partitions holding
files pointed to by symbolic links to be mounted. If the shell variable is
set to or or any combination thereof (e.g., they are used as flags to
making it act like ls -xF ls -Fa ls -FA or a combination, for example On
machines where is not the default, acts like unless contains an in which
case it acts like passes its arguments to if it is given any switches, so
generally does the right thing. The builtin can list files using different
colors depending on the file type or extension. See the shell variable and
the and environment variables. The first form migrates the process or job
to the site specified or the default site determined by the system path.
(TCF only) The second form is equivalent to in that it migrates the current
process to the specified site. Migrating the shell itself can cause
unexpected behavior, because the shell does not like to lose its tty. (TCF
only) Equivalent to as per Available only if the shell was so compiled; see
the shell variable. Increments the scheduling priority for the shell by
or, without by 4. With runs at the appropriate priority. The greater the
the less cpu the process gets. The super-user may decrement the priority
by using is always executed in a sub-shell, and the restrictions placed on
commands in simple statements apply. With runs such that it will ignore
hangup signals. Note that commands may set their own response to hangups,
overriding Without an argument, causes the non-interactive shell only to
ignore hangups for the remainder of the script. See also and the builtin
command. Causes the shell to notify the user asynchronously when the
status of any of the specified jobs (or, without the current job) changes,
instead of waiting until the next prompt as is usual. may be a number, a
string, or as described under See also the shell variable. Controls the
action of the shell on interrupts. Without arguments, restores the default
action of the shell on interrupts, which is to terminate shell scripts or
to return to the terminal command input level. With causes all interrupts
to be ignored. With causes the shell to execute a when an interrupt is
received or a child process terminates because it was interrupted. is
ignored if the shell is running detached and in system startup files (see
where interrupts are disabled anyway. Without arguments, pops the
directory stack and returns to the new top directory. With a number
discards the th entry in the stack. Finally, all forms of print the final
directory stack, just like The shell variable can be set to prevent this
and the flag can be given to override The and flags have the same effect on
as on (+) Prints the names and values of all environment variables or, with
the value of the environment variable Without arguments, exchanges the top
two elements of the directory stack. If is set, without arguments acts as
like (+) With pushes the current working directory onto the directory stack
and changes to If is it is interpreted as the previous working directory
(see (+) If is set, removes any instances of from the stack before pushing
it onto the stack. (+) With a number rotates the th element of the
directory stack around to be the top element and changes to it. If is set,
however, extracts the th directory, pushes it onto the top of the stack and
changes to it. (+) Finally, all forms of print the final directory stack,
just like The shell variable can be set to prevent this and the flag can be
given to override The and flags have the same effect on as on (+) Causes
the internal hash table of the contents of the directories in the variable
to be recomputed. This is needed if the shell variable is not set and new
commands are added to directories in while you are logged in. With a new
command will be found automatically, except in the special case where
another command of the same name which is located in a different directory
already exists in the hash table. Also flushes the cache of home
directories built by tilde expansion. The specified which is subject to
the same restrictions as the in the one line statement above, is executed
times. I/O redirections occur exactly once, even if is 0. Changes the
rootnode to so that will be interpreted as (Domain/OS only) (+) The first
form prints the scheduled-event list. The shell variable may be set to
define the format in which the scheduled-event list is printed. The second
form adds to the scheduled-event list. For example, > sched 11:00 echo
It\'s eleven o\'clock. causes the shell to echo at 11 AM. The time may be
in 12-hour AM/PM format > sched 5pm set prompt='[%h] It\'s after 5; go
home: >' or may be relative to the current time: > sched +2:15
/usr/lib/uucp/uucico -r1 -sother A relative time specification may not use
AM/PM format. The third form removes item from the event list: > sched 1
Wed Apr 4 15:42 /usr/lib/uucp/uucico -r1 -sother 2 Wed Apr 4 17:00 set
prompt=[%h] It's after 5; go home: > > sched -2 > sched 1 Wed Apr 4 15:42
/usr/lib/uucp/uucico -r1 -sother A command in the scheduled-event list is
executed just before the first prompt is printed after the time when the
command is scheduled. It is possible to miss the exact time when the
command is to be run, but an overdue command will execute at the next
prompt. A command which comes due while the shell is waiting for user
input is executed immediately. However, normal operation of an already-
running command will not be interrupted so that a scheduled-event list
element may be run. This mechanism is similar to, but not the same as, the
command on some Unix systems. Its major disadvantage is that it may not
run a command at exactly the specified time. Its major advantage is that
because runs directly from the shell, it has access to shell variables and
other structures. This provides a mechanism for changing one's working
environment based on the time of day. (+) The first form of the command
prints the value of all shell variables. Variables which contain more than
a single word print as a parenthesized word list. The second form sets to
the null string. The third form sets to the single The fourth form sets to
the list of words in In all cases the value is command and filename
expanded. If is specified, the value is set read-only. If or are
specified, set only unique words keeping their order. prefers the first
occurrence of a word, and the last. The fifth form sets the 'th component
of to this component must already exist. The sixth form lists only the
names of all shell variables that are read-only. The seventh form makes
read-only, whether or not it has a value. The eighth form is the same as
the third form, but make read-only at the same time. These arguments can
be repeated to set and/or make read-only multiple variables in a single set
command. Note, however, that variable expansion happens for all arguments
before any setting occurs. Note also that can be adjacent to both and or
separated from both by whitespace, but cannot be adjacent to only one or
the other. See also the builtin command. Without arguments, prints the
names and values of all environment variables. With sets the environment
variable to or, without to the null string. Equivalent to (Mach only) Sets
the system execution path. (TCF only) Tells the shell to believe that the
terminal capability (as defined in has the value No sanity checking is
done. Concept terminal users may have to to get proper wrapping at the
rightmost column. (+) Controls which tty modes (see the shell does not
allow to change. or tells to act on the or set of tty modes respectively;
without or is used. Without other arguments, lists the modes in the chosen
set which are fixed on or off The available modes, and thus the display,
vary from system to system. With lists all tty modes in the chosen set
whether or not they are fixed. With or fixes on or off or removes control
from in the chosen set. For example, fixes mode on and allows commands to
turn mode on or off, both when the shell is executing commands. Set the
experimental version prefix to or removes it if is omitted. (TCF only)
Without arguments, discards and shifts the members of to the left. It is
an error for not to be set or to have fewer than one word as value. With
performs the same function on The shell reads and executes commands from
The commands are not placed on the history list. If any are given, they
are placed in (+) commands may be nested; if they are nested too deeply the
shell may run out of file descriptors. An error in a at any level
terminates all nested commands. With commands are placed on the history
list instead of being executed, much like Stops the specified jobs or
processes which are executing in the background. may be a number, a
string, or as described under There is no default entering just does not
stop the current job. Causes the shell to stop in its tracks, much as if
it had been sent a stop signal with This is most often used to stop shells
started by Each case label is successively matched, against the specified
which is first command and filename expanded. The file metacharacters and
may be used in the case labels, which are variable expanded. If none of
the labels match before a label is found, then the execution begins after
the label. Each case label and the label must appear at the beginning of a
line. The command causes execution to continue after the Otherwise control
may fall through case labels and default labels as in C. If no label
matches and there is no default, execution continues after the Lists the
values of all terminal capabilities (see Tests if (or the current value of
if no is given) has an entry in the hosts or database. Prints the terminal
type to stdout and returns 0 if an entry is present otherwise returns 1.
Executes (which must be a simple command, not an alias, a pipeline, a
command list or a parenthesized command list) and prints a time summary as
described under the variable. If necessary, an extra shell is created to
print the time statistic when the command completes. Without prints a time
summary for the current shell and its children. Sets the file creation
mask to which is given in octal. Common values for the mask are 002,
giving all access to the group and read and execute access to others, and
022, giving read and execute access to the group and others. Without
prints the current file creation mask. Removes all aliases whose names
match Thus removes all aliases. It is not an error for nothing to be ed.
Removes all completions whose names match Thus removes all completions. It
is not an error for nothing to be d. Disables use of the internal hash
table to speed location of executed programs. Sets the universe to
(Masscomp/RTU only) Removes the limitation on or, if no is specified, all
limitations. With the corresponding hard limits are removed. Only the
super-user may do this. Note that may not exit successful, since most
systems do not allow to be unlimited. With errors are ignored. Removes
all variables whose names match unless they are read-only. Thus removes
all variables unless they are read-only; this is a bad idea. It is not an
error for nothing to be Removes all environment variables whose names match
Thus removes all environment variables; this is a bad idea. It is not an
error for nothing to be ed. Without arguments, prints With sets to With
and executes under may be or (Domain/OS only) The shell waits for all
background jobs. If the shell is interactive, an interrupt will disrupt
the wait and cause the shell to print the names and job numbers of all
outstanding jobs. Sets the universe to (Convex/OS only) An alternate name
for the builtin command. Available only if the shell was so compiled; see
the shell variable. Reports all known instances of including aliases,
builtins and executables in Displays the command that will be executed by
the shell after substitutions, searching, etc. The builtin command is just
like but it correctly reports aliases and builtins and is 10 to 100 times
faster. See also the editor command. Executes the commands between the
and the matching while (an expression, as described under evaluates non-
zero. and must appear alone on their input lines. and may be used to
terminate or continue the loop prematurely. If the input is a terminal,
the user is prompted the first time through the loop as with If set, each
of these aliases executes automatically at the indicated time. They are
all initially undefined. Supported special aliases are: Runs when the
shell wants to ring the terminal bell. Runs after every change of working
directory. For example, if the user is working on an X window system using
and a re-parenting window manager that supports title bars such as and does
> alias cwdcmd 'echo -n "^[]2;${HOST}:$cwd ^G"' then the shell will change
the title of the running to be the name of the host, a and the full current
working directory. A fancier way to do that is > alias cwdcmd 'echo -n
"^[]2;${HOST}:$cwd^G^[]1;${HOST}^G"' This will put the hostname and working
directory on the title bar but only the hostname in the icon manager menu.
Note that putting a or in may cause an infinite loop. It is the author's
opinion that anyone doing so will get what they deserve. Runs before each
command gets executed, or when the command changes state. This is similar
to but it does not print builtins. > alias jobcmd 'echo -n
"^[]2\;\!#:q^G"' then executing will put the command string in the xterm
title bar. Invoked by the editor command. The command name for which help
is sought is passed as sole argument. For example, if one does > alias
helpcommand '\!:1 --help' then the help display of the command itself will
be invoked, using the GNU help calling convention. Currently there is no
easy way to account for various calling conventions (e.g., the customary
Unix except by using a table of many commands. Runs every minutes. This
provides a convenient means for checking on common but infrequent changes
such as new mail. For example, if one does > set tperiod = 30 > alias
periodic checknews then the program runs every 30 minutes. If is set but
is unset or set to 0, behaves like Runs just before each prompt is printed.
For example, if one does > alias precmd date then runs just before the
shell prompts for each command. There are no limits on what can be set to
do, but discretion should be used. Runs before each command gets executed.
> alias postcmd 'echo -n "^[]2\;\!#:q^G"' then executing will put the
command string in the xterm title bar. Specifies the interpreter for
executable scripts which do not themselves specify an interpreter. The
first word should be a full path name to the desired interpreter (e.g., or
The variables described in this section have special meaning to the shell.
The shell sets and at startup; they do not change thereafter unless changed
by the user. The shell updates and when necessary, and sets on logout.
The shell synchronizes and with the environment variables of the same
names: whenever the environment variable changes the shell changes the
corresponding shell variable to match (unless the shell variable is read-
only) and vice versa. Note that although and have identical meanings, they
are not synchronized in this manner, and that the shell automatically
converts between the different formats of and Supported special shell
variables are: If set, filename completion adds to the end of directories
and a space to the end of normal files when they are matched exactly. Set
by default. If set, 's autolock feature uses its value instead of the
local username for kerberos authentication. If set, all times are shown in
12-hour AM/PM format. This variable selects what is propagated to the
value of the variable. For more information see the description of the
variable below. The arguments to the shell. Positional parameters are
taken from i.e., is replaced by etc. Set by default, but usually empty in
interactive shells. If set, the editor command is invoked automatically
before each completion attempt. If set, the editor command is invoked
automatically before each completion attempt. If this is set to then only
history will be expanded and a second completion will expand filenames. If
set, possibilities are listed after an ambiguous completion. If set to
possibilities are listed only when no new characters are added by
completion. The first word is the number of minutes of inactivity before
automatic logout. The optional second word is the number of minutes of
inactivity before automatic locking. When the shell automatically logs
out, it prints sets the variable to and exits. When the shell
automatically locks, the user is required to enter their password to
continue working. Five incorrect attempts result in automatic logout. Set
to (automatic logout after 60 minutes, and no locking) by default in login
and superuser shells, but not if the shell thinks it is running under a
window system (i.e., the environment variable is set), the tty is a
pseudo-tty (pty) or the shell was not so compiled (see the shell variable).
Unset or set it to to disable automatic logout. See also the and shell
variables. If set, the internal hash table of the contents of the
directories in the variable will be recomputed if a command is not found in
the hash table. In addition, the list of available commands will be
rebuilt for each command completion or spelling correction attempt if set
to or respectively; if set to this will be done for both cases. If set,
backslashes (`\') always quote and This may make complex quoting tasks
easier, but it can cause syntax errors in scripts. The file name of the
message catalog. If set, uses as a message catalog instead of default A
list of directories in which should search for subdirectories if they
aren't found in the current directory. If not set, requires a directory
and will not go to the directory if it's omitted. This is set by default.
If set, it enables color display for the builtin and it passes to (or if is
set). Alternatively, it can be set to only or only to enable color for a
specific command. Setting it to nothing is equivalent to setting it to
Color is disabled if the output is not directed to a terminal, unless is
set. If set, it enables color escape sequence for NLS message files, and
display colorful NLS messages. If set, the command which was passed to the
shell with the flag. If set, the shell will evaluate expressions right to
left, like the original If set to the completion becomes case insensitive.
If set to completion ignores case and considers hyphens and underscores to
be equivalent; it will also treat periods, hyphens and underscores and as
word separators. If set to completion matches uppercase and underscore
characters explicitly and matches lowercase and hyphens in a case-
insensitive manner; it will treat periods, hyphens and underscores as word
separators. If set to a list of commands, the shell will continue the
listed commands, instead of starting a new one. Same as continue, but the
shell will execute: echo `pwd` $argv > ~/.<cmd>_pause; %<cmd> If set to
commands are automatically spelling-corrected. If set to commands are
automatically completed. If set to the entire command line is corrected.
If set, newlines and carriage returns in command substitution are replaced
by spaces. Set by default. The full pathname of the current directory.
See also the and shell variables. If set, extracts the th directory from
the directory stack rather than rotating it to the top. The default
location in which and look for a history file. If unset, is used. Because
only is normally sourced before should be set in rather than An array of
all the directories on the directory stack. is the current working
directory, the first directory on the stack, etc. Note that the current
working directory is but in directory stack substitutions, etc. One can
change the stack arbitrarily by setting but the first element (the current
working directory) is always correct. See also the and shell variables.
Has an effect only if is listed as part of the shell variable. If set to
it enables display and editing EUC-kanji(Japanese) code. If set to it
enables display and editing Shift-JIS(Japanese) code. If set to it enables
display and editing Big5(Chinese) code. If set to it enables display and
editing Utf8(Unicode) code. If set to 256 characters in the following
format, it enables display and editing of original multi-byte code format:
Each character in the 256 character value corresponds (from left to right)
to the ASCII codes 0x00, 0x01, 0x02, ..., 0xfd, 0xfe, 0xff at the same
index. Each character is set to number 0, 1, 2 or 3, with the meaning: Not
used for multi-byte characters. Used for the first byte of a multi-byte
character. Used for the second byte of a multi-byte character. Used for
both the first byte and second byte of a multi-byte character. For
example, if set to 256 characters starting with the value is interpreted
as: The GNU coreutils version of cannot display multi-byte filenames
without the option. If you are using this version, set the second word of
dspmbyte to If not, for example, cannot display multi-byte filenames. Note
that this variable can only be used if KANJI and DSPMBYTE has been defined
at compile time. If set, removes any instances of from the stack before
pushing it onto the stack. If set, each command with its arguments is
echoed just before it is executed. For non-builtin commands all expansions
occur before echoing. Builtin commands are echoed before command and
filename substitution, because these substitutions are then done
selectively. Set by the command line option. The style of the builtin.
May be set to: Don't echo a newline if the first argument is the default
for Recognize backslashed escape sequences in echo strings. Recognize both
the flag and backslashed escape sequences; the default for Recognize
neither. Set by default to the local system default. The BSD and System V
options are described in the man pages on the appropriate systems. If set,
the command-line editor is used. Set by default in interactive shells. A
list of command names for the editor command to match. If not set, the if
unset) and if unset) environment variables will be used instead. If set,
the and prompt sequences (see the shell variable) indicate skipped
directories with an ellipsis instead of The user's effective user ID. The
first matching passwd entry name corresponding to the effective user ID.
Lists file name suffixes to be ignored by completion. In completion is
always used and this variable is ignored by default. If is unset, then the
traditional completion is used. If set in filename completion is used.
The user's real group ID. If set, wild-card glob patterns will match files
and directories beginning with except for and If set, the and file glob
patterns will match any string of characters including traversing any
existing sub-directories. For example, will list all the .c files in the
current directory tree. If used by itself, it will match zero or more
sub-directories. For example, will list any file named in the directory
tree; whereas will match any file in the directory tree ending in To
prevent problems with recursion, the glob-pattern will not descend into a
symbolic link containing a directory. To override this, use The user's
group name. If set, the incremental search match (in and and the region
between the mark and the cursor are highlighted in reverse video.
Highlighting requires more frequent terminal writes, which introduces extra
overhead. If you care about terminal performance, you may want to leave
this unset. A string value determining the characters used in The first
character of its value is used as the history substitution character,
replacing the default character The second character of its value replaces
the character in quick substitutions. Controls handling of duplicate
entries in the history list. If set to only unique history events are
entered in the history list. If set to and the last history event is the
same as the current command, then the current command is not entered in the
history. If set to and the same event is found in the history list, that
old event gets erased and the current one gets inserted. Note that the and
options renumber history events so there are no gaps. The default location
in which and look for a history file. If unset, is used. is useful when
sharing the same home directory between different machines, or when saving
separate histories on different terminals. Because only is normally
sourced before should be set in rather than If set, builtin and editor
commands and the mechanism use the literal (unexpanded) form of lines in
the history list. See also the editor command. The first word indicates
the number of history events to save. The optional second word (+)
indicates the format in which history is printed; if not given, is used.
The format sequences are described below under note the variable meaning of
Set to by default. Initialized to the home directory of the invoker. The
filename expansion of refers to this variable. If set to the empty string
or and the input device is a terminal, the command (usually generated by
the user by typing on an empty line) causes the shell to print instead of
exiting. This prevents the shell from accidentally being killed.
Historically this setting exited after 26 successive EOF's to avoid
infinite loops. If set to a number the shell ignores - 1 consecutive s and
exits on the th (+). If unset, is used, i.e., the shell exits on a single
If set, the shell treats a directory name typed as a command as though it
were a request to change to that directory. If set to the change of
directory is echoed to the standard output. This behavior is inhibited in
non-interactive shell scripts, or for command strings with more than one
word. Changing directory takes precedence over executing a like-named
command, but it is done after alias substitutions. Tilde and variable
expansions work as expected. If set to or puts the editor into that input
mode at the beginning of each line. Controls handling of duplicate entries
in the kill ring. If set to only unique strings are entered in the kill
ring. If set to and the last killed string is the same as the current
killed string, then the current string is not entered in the ring. If set
to and the same string is found in the kill ring, the old string is erased
and the current one is inserted. Indicates the number of killed strings to
keep in memory. Set to by default. If unset or set to less than the shell
will only keep the most recently killed string. Strings are put in the
killring by the editor commands that delete (kill) strings of text, e.g.
etc, as well as the command. The editor command will yank the most
recently killed string into the command-line, while (see can be used to
yank earlier killed strings. If set to or or any combination thereof
(e.g., they are used as flags to making it act like ls -xF ls -Fa ls -FA or
a combination, for example If the first word contains shows all files (even
if they start with a If the first word contains shows all files but and If
the first word contains sorts across instead of down. If the second word
of is set, it is used as the path to If set, all jobs are listed when a job
is suspended. If set to the listing is in long format. If set, the
builtin command shows the type of file to which each symbolic link points.
The maximum number of items which the editor command will list without
asking first. The maximum number of rows of items which the editor command
will list without asking first. Set by the shell if it is a login shell.
Setting or unsetting it within a shell has no effect. See also Set by the
shell to before a normal logout, before an automatic logout, and if the
shell was killed by a hangup signal (see See also the shell variable. A
list of files and directories to check for incoming mail, optionally
preceded by a numeric word. Before each prompt, if 10 minutes have passed
since the last check, the shell checks each file and displays (or, if
contains multiple files, if the filesize is greater than zero in size and
has a modification time greater than its access time. If you are in a
login shell, then no mail file is reported unless it has been modified
after the time the shell has started up, to prevent redundant
notifications. Most login programs will tell you whether or not you have
mail when you log in. If a file specified in is a directory, the shell
will count each file within that directory as a separate message, and will
report or as appropriate. This functionality is provided primarily for
those systems which store mail in this manner, such as the Andrew Mail
System. If the first word of is numeric it is taken as a different mail
checking interval, in seconds. Under very rare circumstances, the shell
may report instead of If set to completion never beeps. If set to it beeps
only when there is no match. If set to it beeps when there are multiple
matches. If set to it beeps when there is one exact and other longer
matches. If unset, is used. If set, beeping is completely disabled. See
also If set, restrictions are placed on output redirection to insure that
files are not accidentally destroyed and that redirections refer to
existing files, as described in the section. If contains an interacive
confirmation is presented, rather than an error. If contains is allowed on
empty files. If set, disable the printing of in the time specifiers at the
change of hour. If set, and are inhibited. This is most useful in shell
scripts which do not deal with filenames, or after a list of filenames has
been obtained and further expansions are not desirable. If set and the
shell supports Kanji (see the shell variable), it is disabled so that the
meta key can be used. If set, a or which does not match any existing files
is left untouched rather than causing an error. It is still an error for
the substitution to be malformed. For example, still gives an error. A
list of directories (or glob-patterns which match directories; see that
should not be during a completion operation. This is usually used to
exclude directories which take too much time to for example If set, the
shell announces job completions asynchronously. The default is to present
job completions just before printing a prompt. The user's real
organization ID. (Domain/OS only) The old working directory, equivalent to
the used by and See also the and shell variables. If set, enable the
printing of padding '0' for hours, in 24 and 12 hour formats. E.g., versus
To retain compatibily with older versions numeric variables starting with 0
are not interpreted as octal. Setting this variable enables proper octal
parsing. A list of directories in which to look for executable commands.
A null word specifies the current directory. If there is no variable then
only full path names will execute. is set by the shell at startup from the
environment variable or, if does not exist, to a system-dependent default,
such as The shell may put first or last in or omit it entirely depending on
how it was compiled; see the shell variable. A shell which is given
neither the nor the option hashes the contents of the directories in after
reading and each time is reset. If one adds a new command to a directory
in while the shell is active, one may need to do a for the shell to find
it. If set and an interactive program exits with a non-zero status, the
shell prints The string which is printed before reading each command from
the terminal. may include any of the following formatting sequences (+),
which are replaced by the given information: The current working directory.
The current working directory, but with one's home directory represented by
and other users' home directories represented by as per substitution
happens only if the shell has already used in a pathname in the current
session. The trailing component of the current working directory, or
trailing components if a digit is given. If begins with the number of
skipped components precede the trailing component(s) in the format If the
shell variable is set, skipped components are represented by an ellipsis so
the whole becomes substitution is done as in above, but the component is
ignored when counting trailing components. Like but without substitution.
The current history event number. The full hostname. The hostname up to
the first Start (stop) standout mode. Start (stop) boldfacing mode. Start
(stop) underline mode. The time of day in 12-hour AM/PM format. Like but
in 24-hour format (but see the shell variable). The time of day in 12-hour
AM/PM format, with seconds. Like but in 24-hour format (but see the shell
variable). is parsed as in is parsed as in A single The user name. The
effective user name. The number of jobs. The weekday in format. The day
in format. The month in format. The month in format. The year in format.
The year in format. The shell's tty. Clears from the end of the prompt to
end of the display or the end of the line. Expands the shell or
environment variable name immediately after the (or the first character of
the shell variable) for normal users, (or the second character of for the
superuser. Includes as a literal escape sequence. It should be used only
to change terminal attributes and should not move the cursor location.
This cannot be the last sequence in The return code of the command executed
just before the prompt. In the status of the parser. In the corrected
string. In the history string. and are available in only eight-bit-clean
shells; see the shell variable. The bold, standout and underline sequences
are often used to distinguish a superuser shell. For example, If or is
used, and is not set, then print on the change of hour (i.e, minutes)
instead of the actual time. Set by default to in interactive shells. The
string with which to prompt in and loops and after lines ending in The same
format sequences may be used as in note the variable meaning of Set by
default to in interactive shells. The string with which to prompt when
confirming automatic spelling correction. The same format sequences may be
used as in note the variable meaning of Set by default to in interactive
shells. If set (to a two-character string), the formatting sequence in the
shell variable is replaced with the first character for normal users and
the second character for the superuser. If set, without arguments does
like If set, and do not print the directory stack. If set, completion
completes on an exact match even if a longer match is possible. If set,
command listing displays only files in the path that are executable. Slow.
If set, the user is prompted before is executed. The string to print on
the right-hand side of the screen (after the command input) when the prompt
is being displayed on the left. It recognizes the same formatting
characters as It will automatically disappear and reappear as necessary, to
ensure that command input isn't obscured, and will appear only if the
prompt, command input, and itself will fit together on the first line. If
isn't set, then will be printed after the prompt and before the command
input. If set, the shell does before exiting. If the first word is set to
a number, at most that many directory stack entries are saved. If set, the
shell does before exiting. If the first word is set to a number, at most
that many lines are saved. (The number should be less than or equal to the
number entries; if it is set to greater than the number of settings, only
entries will be saved.) If the second word is set to the history list is
merged with the existing history file instead of replacing it (if there is
one) and sorted by time stamp and the most recent events are retained. If
the second word is set to and the third word is set to the history file
update will be serialized with other shell sessions that would possibly
like to merge history at exactly the same time. (+) The format in which the
builtin command prints scheduled events; if not given, is used. The format
sequences are described above under note the variable meaning of The file
in which the shell resides. This is used in forking shells to interpret
files which have execute bits set, but which are not executable by the
system. (See the description of Initialized to the (system-dependent) home
of the shell. The number of nested shells. Reset to 1 in login shells.
See also The exit status from the last command or backquote expansion, or
any command in a pipeline is propagated to (This is also the default
behavior.) This default does not match what POSIX mandates (to return the
status of the last command only). To match the POSIX behavior, you need to
unset If the variable is unset, the exit status of a pipeline is determined
only from the last command in the pipeline, and the exit status of a
backquote expansion is propagated to If a command terminated abnormally,
then 0200 is added to the status. Builtin commands which fail return exit
status all other builtin commands return status Can be set to several
different values to control symbolic link resolution: If set to whenever
the current directory changes to a directory containing a symbolic link, it
is expanded to the real name of the directory to which the link points.
This does not work for the user's home directory; this is a bug. If set to
the shell tries to construct a current directory relative to the current
directory before the link was crossed. This means that through a symbolic
link and then returns one to the original directory. This affects only
builtin commands and filename completion. If set to the shell tries to fix
symbolic links by actually expanding arguments which look like path names.
This affects any command, not just builtins. Unfortunately, this does not
work for hard-to-recognize filenames, such as those embedded in command
options. Expansion may be prevented by quoting. While this setting is
usually the most convenient, it is sometimes misleading and sometimes
confusing when it fails to recognize an argument which should be expanded.
A compromise is to use and use the editor command (bound by default to when
necessary. Some examples are in order. First, let's set up some play
directories: > cd /tmp > mkdir from from/src to > ln -s from/src to/dst
Here's the behavior with unset, > cd /tmp/to/dst; echo $cwd /tmp/to/dst >
cd ..; echo $cwd /tmp/from Here's the behavior with set to > cd
/tmp/to/dst; echo $cwd /tmp/from/src > cd ..; echo $cwd /tmp/from Here's
the behavior with set to > cd /tmp/to/dst; echo $cwd /tmp/to/dst > cd ..;
echo $cwd /tmp/to Here's the behavior with set to > cd /tmp/to/dst; echo
$cwd /tmp/to/dst > cd ..; echo $cwd /tmp/to > cd /tmp/to/dst; echo $cwd
/tmp/to/dst > cd ".."; echo $cwd /tmp/from > /bin/echo .. /tmp/to >
/bin/echo ".." .. Note that expansion: Works just like for builtins like
Is prevented by quoting. Happens before filenames are passed to non-
builtin commands. The version number of the shell in the format where is
the major release number, the current version, and the patchlevel. The
terminal type. Usually set in as described under If set to a number, then
the builtin executes automatically after each command which takes more than
that many CPU seconds. If there is a second word, it is used as a format
string for the output of the builtin. (u) The following sequences may be
used in the format string: The time the process spent in user mode in cpu
seconds. The time the process spent in kernel mode in cpu seconds. The
elapsed (wall clock) time in seconds. The CPU percentage computed as (%U +
%S) / %E. Number of times the process was swapped. The average amount in
(shared) text space used in Kbytes. The average amount in (unshared)
data/stack space used in Kbytes. The total space used (%X + %D) in Kbytes.
The maximum memory the process had in use at any time in Kbytes. The
number of major page faults (page needed to be brought from disk). The
number of minor page faults. The number of input operations. The number
of output operations. The number of socket messages received. The number
of socket messages sent. The number of signals received. The number of
voluntary context switches (waits). The number of involuntary context
switches. Only the first four sequences are supported on systems without
BSD resource limit functions. The default time format is for systems that
support resource usage reporting and for systems that do not. Under
Sequent's DYNIX/ptx, and are not available, but the following additional
sequences are: The number of system calls performed. The number of pages
which are zero-filled on demand. The number of times a process's resident
set size was increased by the kernel. The number of times a process's
resident set size was decreased by the kernel. The number of read system
calls performed. The number of write system calls performed. The number
of reads from raw disk devices. The number of writes to raw disk devices.
and the default time format is Note that the CPU percentage can be higher
than 100% on multi-processors. The period, in minutes, between executions
of the special alias. The name of the tty, or empty if not attached to
one. The user's real user ID. The user's login name. If set, causes the
words of each command to be printed, after history substitution (if any).
Set by the command line option. The version ID stamp. It contains the
shell's version number (see origin, release date, vendor, operating system
and machine (see and and a comma-separated list of options which were set
at compile time. Options which are set by default in the distribution are
noted. Supported options include: The shell is eight bit clean; default.
The shell is not eight bit clean. The shell is multi-byte encoding clean
(like UTF-8). The system's NLS is used; default for systems with NLS.
Login shells execute before instead of after and before instead of after
and is put last in for security; default. is omitted from for security.
-style editing is the default rather than -style. Login shells drop DTR
when exiting. is a synonym for and is an alternate name for is enabled;
default. Kanji is used if appropriate according to locale settings, unless
the shell variable is set. The system's is used. The convention is
emulated when executing shell scripts. The builtin is available. The
shell attempts to set the environment variable. The shell verifies your
password with the kerberos server if local authentication fails. The shell
variable or the environment variable override your local username if set.
An administrator may enter additional strings to indicate differences in
the local version. If unset, various key bindings change behavior to be
more -style: word boundaries are determined by versus other characters. If
set, various key bindings change behavior to be more -style: word
boundaries are determined by versus whitespace versus other characters;
cursor behavior depends upon current vi mode (command, delete, insert,
replace). This variable is unset by and set by may be explicitly set or
unset by the user after those operations if required. If set, a screen
flash is used rather than the audible bell. See also A list of
user/terminal pairs to watch for logins and logouts. If either the user is
all terminals are watched for the given user and vice versa. Setting to
watches all users and terminals. For example, set watch = (george ttyd1
any console $user any) reports activity of the user on any user on the
console, and oneself (or a trespasser) on any terminal. Logins and logouts
are checked every 10 minutes by default, but the first word of can be set
to a number to check every so many minutes. For example, set watch = (1
any any) reports any login/logout once every minute. For the impatient,
the builtin command triggers a report at any time. All current logins are
reported (as with the builtin) when is first set. The shell variable
controls the format of reports. The format string for messages. The
following sequences are replaced by the given information: The name of the
user who logged in/out. The observed action, i.e., or The terminal (tty)
on which the user logged in/out. The full hostname of the remote host, or
if the login/logout was from the local host. The hostname of the remote
host up to the first The full name is printed if it is an IP address or an
X Window System display. and are available on only systems that store the
remote hostname in If unset, is used, or on systems which don't store the
remote hostname. A list of non-alphanumeric characters to be considered
part of a word by the etc., editor commands. If unset, the default value
is determined based on the state of if is unset, is used as the default; if
is set, is used as the default. Equivalent to the shell variable. Color
sequences for are normally disabled if the output is not directed to a
terminal. This can be overridden by setting this variable, which also
changes the invocation of to use instead of Note that must be set for this
environment variable to be effective; by itself does not enable color Set
by to the current command line when invoking programs for the mode See in
The number of columns in the terminal. See Used by X Window System (see If
set, the shell does not set The pathname to a default editor. Used by the
editor command if the the shell variable is unset. See also the
environment variable. Equivalent to the shell variable. Equivalent to the
shell variable. Initialized to the name of the machine on which the shell
is running, as determined by the system call. Initialized to the type of
machine on which the shell is running, as determined at compile time. This
variable is obsolete and will be removed in a future version. A list of
directories in which the editor command looks for command documentation.
Gives the preferred character environment. See If set, only ctype
character handling is changed. See The number of lines in the terminal.
See One of two environment variables that may be used to define the per-
file colors used by (along with This variable is used by some BSD versions
of On startup, takes priority over If both or are the most recent is used.
If is while is still then is parsed again (with any warnings suppressed) to
reapply its settings. This variable is a 22 character string containing a
concatenation of 11 pairs of the format where is the foreground color and
is the background color. If fewer than 11 pairs are provided, default
colors are used for the remaining entries. If more than 11 pairs are
provided, the extra values are ignored. The order of the color attribute
pairs to the equivalent variable, the file type, and default color, is as
follows: The color code designators are as follows: Black. Red. Green.
Yellow (or brown). Blue. Magenta. Cyan. Light grey. Bold black,
usually shows up as dark grey. Bold red. Bold green. Bold yellow. Bold
blue. Bold magenta. Bold cyan. Bold light grey; looks like bright white.
Default foreground or background. Note that the above are standard ANSI
colors. The actual display may differ depending on the color capabilities
of the terminal in use. The default colors are as per the color variables
in and are not the same default colors as those used by some BSD versions
of One of two environment variables that may be used to define the per-file
colors used by (along with This variable is used by the GNU coreutils
version of and may be setup by On startup, takes priority over If both or
are the most recent is used. If is while is still then is parsed again
(with any warnings suppressed) to reapply its settings. The format of this
variable is reminiscent of the file format; a list of expressions of the
form or The first form where is a two-character variable name, supports the
following variables, their associated default ISO 6429 color code or escape
sequences, and file type: You need to include only the variables you want
to change from the default. The second form colorizes file names based on
extension. For example, using ISO 6429 codes, to color all C-language
source files blue you would specify This would color all files ending in in
blue foreground (34) color. Control characters can be written either in
C-style-escaped notation, or in stty-like ^-notation. The C-style notation
adds for Escape, for a normal space character, and for Delete. In
addition, the escape character can be used to override the default
interpretation of and Each filename will be output to the terminal as If
the code is undefined, the sequence will be used instead. This is
generally more convenient to use, but less general. The left code right
code and end codes are provided so you don't have to type common parts over
and over again and to support weird terminals; you will generally not need
to change them at all unless your terminal does not use ISO 6429 color
codes but a different system. If your terminal uses ISO 6429 color codes,
you can compose the type codes (i.e., all except the and codes) from
numerical ISO 6429 color codes separated by For example, is bright green
foreground with default background. The most common ISO 6429 color codes
are: To restore default color. Bold / brighter colors. Underlined text.
Flashing text. Black foreground. Red foreground. Green foreground.
Yellow (or brown) foreground. Blue foreground. Magenta foreground. Cyan
foreground. White (or gray) foreground. Black background. Red
background. Green background. Yellow (or brown) background. Blue
background. Magenta background. Cyan background. White (or gray)
background. Not all ISO 6429 color codes will work on all systems or
display devices. A few terminal programs do not recognize the default end
code properly. If all text gets colorized after you do a directory
listing, try changing the and codes from 0 to the numerical codes for your
standard foreground and background colors. For symbolic links the keyword
can be set to which makes the file color the same as the color of the link
target. The machine type (microprocessor class or machine model), as
determined at compile time. If set, printable characters are not rebound
to See The operating system, as determined at compile time. A list of
directories in which to look for executables. Equivalent to the shell
variable, but in a different format. Equivalent to the shell variable, but
not synchronized to it; updated only after an actual directory change. The
host from which the user has logged in remotely, if this is the case and
the shell is able to determine it. Set only if the shell was so compiled;
see the shell variable. Equivalent to the shell variable. The current
system type. (Domain/OS only) Equivalent to the shell variable. The
terminal capability string. See Equivalent to the shell variable. The
vendor, as determined at compile time. The pathname to a default full-
screen editor. Used by the editor command if the the shell variable is
unset. See also the environment variable. Read first by every shell.
ConvexOS, Stellix and Intel use NeXTs use A/UX, AMIX, Cray and IRIX have no
equivalent in but read this file in anyway. Solaris 2.x does not have it
either, but reads (+) Read by login shells after ConvexOS, Stellix and
Intel use NeXTs use Solaris 2.x uses A/UX, AMIX, Cray and IRIX use Read by
every shell after or its equivalent. Read by every shell, if doesn't
exist, after or its equivalent. This manual uses to mean or, if is not
found, Read by login shells after if is set, but see also Read by login
shells after or The shell may be compiled to read before instead of after
and see the shell variable. Read by login shells after if is set, but see
also Read by login shells at logout. ConvexOS, Stellix and Intel use NeXTs
use A/UX, AMIX, Cray and IRIX have no equivalent in but read this file in
anyway. Solaris 2.x does not have it either, but reads (+) Read by login
shells at logout after or its equivalent. Used to interpret shell scripts
not starting with a Temporary file for Source of home directories for
substitutions. The order in which startup files are read may differ if the
shell was so compiled; see and the shell variable. This manual describes
as a single entity, but experienced users will want to pay special
attention to 's new features. A command-line editor, which supports -style
or -style key bindings. See and Programmable, interactive word completion
and listing. See and the and builtin commands. of filenames, commands and
variables. which perform other useful functions in the middle of typed
commands, including documentation lookup quick editor restarting and
command resolution An enhanced history mechanism. Events in the history
list are time-stamped. See also the command and its associated shell
variables, the previously undocumented event specifier and new modifiers
under the and editor commands and the shell variable. Enhanced directory
parsing and directory stack handling. See the and commands and their
associated shell variables, the description of the and shell variables and
the and editor commands. Negation in glob-patterns. See New and a builtin
which uses them. A variety of including scheduled events, special aliases,
automatic logout and terminal locking, command timing and watching for
logins and logouts. Support for the Native Language System (see OS variant
features (see and the shell variable) and system-dependent file locations
(see Extensive terminal-management capabilities. See New builtin commands
including and New variables that make useful information easily available
to the shell. See the and shell variables and the and environment
variables. A new syntax for including useful information in the prompt
string (see and special prompts for loops and spelling correction (see and
Read-only variables. See In 1964, DEC produced the PDP-6. The PDP-10 was
a later re-implementation. It was re-christened the DECsystem-10 in 1970
or so when DEC brought out the second model, the KI10. TENEX was created
at Bolt, Beranek & Newman (a Cambridge, Massachusetts think tank) in 1972
as an experiment in demand-paged virtual memory operating systems. They
built a new pager for the DEC PDP-10 and created the OS to go with it. It
was extremely successful in academia. In 1975, DEC brought out a new model
of the PDP-10, the KL10; they intended to have only a version of TENEX,
which they had licensed from BBN, for the new box. They called their
version TOPS-20 (their capitalization is trademarked). A lot of TOPS-10
users (`The OPerating System for PDP-10') objected; thus DEC found
themselves supporting two incompatible systems on the same hardware--but
then there were 6 on the PDP-11! TENEX, and TOPS-20 to version 3, had
command completion via a user-code-level subroutine library called ULTCMD.
With version 3, DEC moved all that capability and more into the monitor
(`kernel' for you Unix types), accessed by the COMND% JSYS (`Jump to
SYStem' instruction, the supervisor call mechanism [are my IBM roots also
showing?]). The creator of tcsh was impressed by this feature and several
others of TENEX and TOPS-20, and created a version of csh which mimicked
them. The system limits argument lists to ARG_MAX characters. The number
of arguments to a command which involves filename expansion is limited to
1/6th the number of characters allowed in an argument list. Command
substitutions may substitute no more characters than are allowed in an
argument list. To detect looping, the shell restricts the number of
substitutions on a single line to 20. This manual documents tcsh 6.24.13
(Astron) 2024-06-12.
Original author of IIASA, Laxenburg, Austria.
Job control and directory stack features. HP Labs, 1981.
File name completion. Fairchild, 1983.
Command name recognition/completion. Ohio State CIS Dept., 1983-1993.
Command line editor, prompt routines, new glob syntax and numerous fixes
and speedups. CCI, 1983-4.
Special aliases, directory stack extraction stuff, login/logout watch,
scheduled events, and the idea of the new prompt format. University of
Toronto, 1984.
and builtins and numerous bug fixes, modifications and speedups. Caltech.
Fast storage allocator routines. TRW, 1987.
Incorporated 4.3BSD into Cornell U. EE Dept., 1987-94.
Ports to HPUX, SVR2 and SVR3, a SysV version of getwd.c, SHORT_STRINGS
support and a new version of sh.glob.c. BBN, and OSU, 1988.
A/UX port. NNSC, 1988.
Kuck and Associates, Inc., 1988.
mode cleanup. Rensselaer Polytechnic Institute, 1989.
and ambiguous completion listing. DEC, 1989.
Newlines in the prompt. BBN, 1989.
Purdue Physics, 1989.
Magic space bar history expansion. Intel, 1989.
fixes and additions. Dept. of Computer Science, Keio University, 1989.
Automatic spelling correction and Ellemtel, Sweden, 1990-.
Various bugfixes, improvements and manual updates. Sun Sweden.
and
Interrupt handling fixes. Digital Equipment Corp.
Extended key support. Convex, 1990.
Convex support, lots of bug fixes, save and restore of directory stack.
Apple, 1990.
A/UX 2.0 (re)port. LTH Sweden, 1990.
NLS support and simulated NLS support for non NLS sites, fixes. SICS
Sweden, 1990.
Mach support, 8-bit printing. Sanyo Icon, 1990.
POSIX termio support, SysV limit fixes. Sequent, 1990-91.
Vi mode fixes, expand-line, window change fixes, Symmetry port. Institut
de recherche d'Hydro-Quebec, 1991.
beeping options, modified the history search to search for the whole string
from the beginning of the line to the cursor. Motorola, 1991.
Minix port. Sydney U. Australia, Physics Dept., 1991.
SVR4 job control fixes. 1991-.
Various portability and other fixes. Added (dollar-single-quotes).
Interactive Systems Corp., 1991.
Extended fixes and delete command. MIT, 1991.
ANSIfication fixes, new exec hashing code, imake fixes, 1991-.
Enhanced directory printing in Added and improvements. Manual page
improvements. sterling@netcom.com, 1991-1995.
ETA and Pyramid port, Makefile and lint fixes, addition, and various other
portability changes and bug fixes. 1992.
and 1992.
Coherent port. Mullard Space Science Lab U.K., 1992.
VMS-POSIX port. IBM Corp., 1992.
Walking process group fixes, bug fixes, POSIX file tests, POSIX SIGHUP.
Cray Computer Corp., 1992.
CSOS port. Rutgers University, 1992.
Tek, m88k, Titan and Masscomp ports and fixes. Added autoconf support.
Cornell University, 1992.
OS/2 port. liljeber@kruuna.Helsinki.FI, 1992.
Linux port. NASA Langley Research Center Operations, 1993.
Read-only variables. Yale University, 1993-4.
New man page and tcsh.man2html. Stanford University, 1993.
AFS and HESIOD patches. Silicon Graphics Inc., 1996.
Added implicit cd. 1997.
Ported to Siemens Nixdorf EBCDIC machine. Microsoft, 1997.
Ported to WIN32 (Windows/95 and Windows/NT); wrote all the missing library
and message catalog code to interface to Windows. 1998.
Color ls additions. Bryan Dunlap, Clayton Elwell, Karl Kleinpaste, Bob
Manson, Steve Romig, Diana Smetters, Bob Sutterfield, Mark Verber,
Elizabeth Zwicky and all the other people at Ohio State for suggestions and
encouragement All the people on the net, for putting up with, reporting
bugs in, and suggesting new additions to each and every version Richard M.
Alderson III, for writing the section When a suspended command is
restarted, the shell prints the directory it started in if this is
different from the current directory. This can be misleading (i.e., wrong)
as the job may have changed directories internally. Shell builtin
functions are not stoppable/restartable. Command sequences of the form are
also not handled gracefully when stopping is attempted. If you suspend the
shell will then immediately execute This is especially noticeable if this
expansion results from an It suffices to place the sequence of commands in
's to force it to a subshell, i.e., Control over tty output after processes
are started is primitive; perhaps this will inspire someone to work on a
good virtual terminal interface. In a virtual terminal interface much more
interesting things could be done with output control. Alias substitution
is most often used to clumsily simulate shell procedures; shell procedures
should be provided rather than aliases. Control structures should be
parsed rather than being recognized as built-in commands. This would allow
control commands to be placed anywhere, to be combined with and to be used
with and metasyntax. doesn't ignore here documents when looking for its It
should be possible to use the modifiers on the output of command
substitutions. The screen update for lines longer than the screen width is
very poor if the terminal cannot move the cursor up (i.e., terminal type
and don't need to be environment variables. Glob-patterns which do not use
or or which use or are not negated correctly. The single-command form of
does output redirection even if the expression is false and the command is
not executed. includes file identification characters when sorting
filenames and does not handle control characters in filenames well. It
cannot be interrupted. Command substitution supports multiple commands and
conditions, but not cycles or backward s. Report bugs at preferably with
fixes. If you want to help maintain and test tcsh, add yourself to the
mailing list in
