SGREP(1) SGREP(1)
NAME
sgrep - search a file for a structured pattern
SYNOPSIS
sgrep [-aCcDdhilNnPqSsTtV] [-O filename] [-o "format"] [-p
preprocessor] [-e] expression [filename ...]
sgrep [-aCcDdhilNnPqSsTtV] [-O filename] [-o "format"] [ -p
preprocessor] -f filename [-e expression] [filename ...]
sgrep -h
DESCRIPTION
sgrep (structured grep) is a tool for searching text files and
filtering text streams using structural criteria. The data model of
sgrep is based on regions, which are non-empty substrings of text.
Regions are typically occurrences of constant strings or meaningful
text elements, which are recognizable through some delimiting strings.
Regions can be arbitrarily long, arbitrarily overlapping, and
arbitrarily nested.
sgrep uses patterns called region expressions to express which regions
of the input text are output to standard output. The selection of
regions is based on mutual containment and ordering conditions of the
regions, expressed by the region expression.
Region expressions are read by default first from file $HOME/.sgreprc,
or if it doesn't exist, from file /usr/lib/sgreprc, and then from the
command line. Different behavior can be specified through command line
options.
Input files are processed one by one (i.e., regions cannot extend over
file boundaries), except if the -S flag is given, in which case sgrep
takes the concatenation of the input files as its input text. If no
input files are given, sgrep reads the standard input. Standard
input can also be specified as an input file by giving hyphen '-' as a
file name.
The selected regions are output in increasing order of their start
positions. If several output regions overlap, a minimal region that
covers them all is output, by default, instead of outputting each of
them separately.
OPTIONS
-a Act as a filter: display the maching regions, possibly formatted
according to the output format, interleaved with the rest of the
text. (See the description of option -o below.)
-C Display copyright notice.
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-c Display only the count of the regions that match the expression.
-D Display verbose progress output. NOTE: This is used for debugging
purposes only and may not function in future versions of sgrep.
-d Display each matching region once, even if the regions overlap or
nest.
-e expression
Search the input text for occurrences of expression.
-f file
Read the region expression from the named file. Filename - refers
to stdin.
-h Display a short help.
-i Ignore case distinctions in phrases.
-l Long output format: precede each output region by a line which
indicates the ordinal number of the region, the name of the file
where the region starts, the length of the region in bytes, the
start and end positions of the region within the entire input
text, the start position of the region within the file containing
the start, and the end position of the region within the file
containing the end.
-N Do not add a newline after the last output region.
-n Suppress reading $HOME/.sgreprc or /usr/lib/sgreprc.
-O file
Read the output format from file. See the description of output
formats below.
-o format
Set the output format. The format is displayed for each output
region with any occurrences of the following place holders
substituted:
%f name of the file containing the start of the region
%s start position of the region
%e end position of the region
%l length of the region in bytes (i.e., %e-%s+1)
%i start position of the region in the file where the region
begins
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%j end position of the region in the file where the region ends
%r text of the region. "%r" is the default output format.
%n gets the ordinal number of the region
-P Display the (preprocessed) region expression without executing
it.
-p preprocessor
Apply preprocessor to the region expression before evaluating it.
-S Stream mode. With this option sgrep considers it's input files as
a continuous stream, so that regions may extend across file
boundaries.
sgrep -S file_1 ... file_n
is similar to
cat file_1 ... file_n | sgrep
except that the latter creates a temporary disk file of the input
stream. Sgrep may use much more memory when run with the -S
option, since then it cannot release its internal region lists
between processing each file.
-s Short output format (default): do not format the text of the
output regions, and display overlapping parts of regions only
once.
-T Display statistics about the execution.
-t Display time usage.
-V Display version information.
-- No more options.
A list of options can be given also as the value of the environment
variable SGREPOPT.
SYNTAX OF EXPRESSIONS
region_expr -> basic_expr
| operator_expr
operator_expr -> region_expr ['not'] 'in' basic_expr
| region_expr ['not'] 'containing' basic_expr
| region_expr ['not'] 'equal' basic_expr
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| region_expr 'or' basic_expr
| region_expr 'extracting' basic_expr
| region_expr '..' basic_expr
| region_expr '_.' basic_expr
| region_expr '._' basic_expr
| region_expr '__' basic_expr
| region_expr 'quote' basic_expr
| region_expr '_quote' basic_expr
| region_expr 'quote_' basic_expr
| region_expr '_quote_' basic_expr
| 'concat' '(' region_expr ')'
| 'inner' '(' region_expr ')'
| 'outer' '(' region_expr ')'
| 'join' '(' integer ',' region_expr ')'
basic_expr -> phrase
| 'start'
| 'end'
| 'chars'
| constant_list
| '(' region_expr ')'
phrase -> '"' char [ char ... ] '"'
constant_list -> '[' ']' | '[' regions ']'
regions -> region
| region regions
region -> '(' integer ',' integer ')'
Note that region expressions are left-associative. This means, for
example, that an expression
'"<a>".."</a>" or "</b>"'
evaluates to the regions starting with "<a>" and ending with "</a>",
or comprising only the string "</b>". In order to obtain the regions
that begin with "<a>" and end with either "</a>" or "</b>", one should
indicate the proper order of evaluation using parentheses:
"<a>".. ("</a>" or "</b>")
Expressions can also contain comments, which start with '#' and extend
to the end of the line. However, a '#'-sign in a phrase does not begin
a comment.
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SEMANTICS OF EXPRESSIONS
The value of an expression is a set of regions of input text that
satisfy the expression.
Value v(basic_expr) of a basic expression:
v(phrase):=
the set of regions of input text whose text equals the text of
the phrase.
v('start'):=
a set consisting of single-character regions for the first
position of each input file. If the -S option is given, the value
is a set containing a single region that comprises the first
character in the input stream.
v('end'):=
a set consisting of single-character regions for the last
position of each input file. If the -S option is given, the value
is a set containing a single region that comprises the last
character in the input stream.
v('chars'):=
a set consisting of all single-character regions.
v([ ]):=
an empty set.
v([(s_1,e_1) (s_1,e_2) ... (s_n,e_n)]):=
a set consisting of regions r_i for each i = 1,...,n, where the
start position of region r_i is s_i and its end position is e_i.
The positions have to be nonnegative integers, and the regions
have to be given in increasing order of their start positions;
regions with a common start positions have to be given in
increasing order of their end positions. The positions are
counted from the first character of each input file, unless the
-S option is given, in which case the positions are counted
starting from the beginning of the input stream. The number of
the first position in a file or a stream is zero.
v('('region_expr')'):= v(region_expr).
Value v(operator_expr) of operator expressions:
v(region_expr 'in' basic_expr):=
the set of the regions in v(region_expr) that are contained in
some region in v(basic_expr). A region x is contained in another
region y if and only if the start position of x is greater than
the start position of y and the end position of x is not greater
than the end position of y, or the end position of x is smaller
than the end position of y and the start position of x is not
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smaller than the start position of y.
v(region_expr 'not' 'in' basic_expr):=
the set of the regions in v(region_expr) that are not contained
in any region in v(basic_expr).
v(region_expr 'containing' basic_expr):=
the set of the regions in v(region_expr) that contain some region
in v(basic_expr).
v(region_expr 'not' 'containing' basic_expr):=
the set of the regions in v(region_expr) that do not contain any
region in v(basic_expr).
v(region_expr 'equal' basic_expr):=
The set of regions, which occur in both v(region_expr) and
v(basic_expr).
v(region_expr 'not equal' basic_expr):=
The set of regions, which occur in v(region_expr) but do not
occur in v(basic_expr).
v(region_expr 'or' basic_expr):=
the set of the regions that appear in v(region_expr) or in
v(basic_expr) or in both.
v(region_expr 'extracting' basic_expr):=
the set of the non-empty regions that are formed of the regions
in v(region_expr) by extracting an overlap with any region in
v(basic_expr). For example, the value of
'[(1,4) (3,6) (7,9)] extracting [(2,5) (4,7)]'
consists of the regions (1,1) and (8,9).
v(region_expr '..' basic_expr):
The value of this expression consists of the regions that can be
formed by pairing regions from v(region_expr) with regions from
v(basic_expr). The pairing is defined as a generalization of the
way how nested parentheses are paired together "from inside out".
For this we need to be able to compare the order of regions,
which may be overlapping and nested. This ordering is defined as
follows.
Let x and y be two regions. We say that region x precedes region
y if the end position of x is smaller than the start position of
y. We say that region x is later than region y if the end
position of x is greater than the end position of y, or if they
end at the same position and the start of x is greater than the
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start of y. Region x is earlier than region y if the start
position of x is smaller than the start position of y, or if they
start at the same position and the end position of x is less than
the end position of y. Now a region x from v(region_expr) and a
region y from v(basic_expr) are paired in expression
v(region_expr '..' basic_expr) if and only if
1. x precedes y,
2. x is not paired with any region from v(basic_expr) which is
earlier than y, and
3. y is not paired with any region from v(region_expr) which is
later than x.
The pairing of regions x and y forms a region that extends from the
start position of x to the end position of y.
v(region_expr '._' basic_expr):
The pairing of the regions from v(region_expr) and the regions
from v(basic_expr) is defined similarly to v(region_expr '..'
basic_expr) above, except that the pairing of regions x and y now
forms a region which extends from the start position of x to the
position immediately preceding the start of y.
v(region_expr '_.' basic_expr):=
The pairing of the regions from v(region_expr) and the regions
from v(basic_expr) is defined similarly to v(region_expr '..'
basic_expr) above, except that the pairing of regions x and y now
forms a region which extends from the position immediately
following the end position of x to the end position of y.
v(region_expr '__' basic_expr):=
The pairing of the regions from v(region_expr) and the regions
from v(basic_expr) is defined similarly to v(region_expr '..'
basic_expr) above, except that now the pairing of regions x and y
forms a region which extends from the text position immediately
following the end of x to the text position immediately preceding
the start of y. Possibly resulting empty regions are excluded
from the result.
v(region_expr 'quote' basic_expr):
The value of this expression consists of the regions that extend
from the start position of a "left-quote region" in
v(region_expr) to the end position of a corresponding "right-
quote region" in v(basic_expr). The regions in the result are
non-nesting and non-overlapping. The left-quote regions and the
right-quote regions are defined as follows:
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+ The earliest region (see above) in v(region_expr) is a
possible left-quote region.
+ For each possible left-quote region x, the earliest region
in v(basic_expr) preceeded by x is its right-quote region.
+ For each right-quote region y in v(basic_expr), the
earliest region in v(region_expr) preceeded by y is a
possible left-quote region.
The below example query finds C-style non-nesting comments:
"/*" quote "*/"
The below example query finds strings between quotation marks:
"\"" quote "\""
(Notice the difference to expression "\"" .. "\"", which would
evaluate to any substring of input text that starts with a quotation
mark and ends with the next quotation mark.)
The variants _quote, quote_ and _quote_ are analogical to the
operators _., ._ and __, in the sense that the "quote regions"
originating from the expression on the side of the underscore _ are
excluded from the result regions. (In the case of _quote_ any
possibly resulting empty regions are excluded from the result.)
v('concat' '(' region_expr ')' ):=
the set of the longest regions of input text that are covered by
the regions in v(region_expr).
v('inner' '(' region_expr ')' ):=
the set of regions in v(region_expr) that do not contain any
other region in v(region_expr). Note that for any region
expression A, the expression inner(A) is equivalent to (A not
containing A).
v('outer' '(' region_expr ')' ):=
the set of regions in v(region_expr) that are not contained in
any other region in v(region_expr). Note that for any region
expression A, the expression outer(A) is equivalent to (A not in
A).
v('join' '(' n ',' region_expr ')' ):
The value of this expression is formed by processing the regions
of v(region_expr) in increasing order of their start positions
(and in increasing order of end positions for regions with a
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common start). Each region r produces a result region beginning
at the start of r and extending to the end of the (n-1)th region
after r. The operation is useful only with non-nesting regions.
Especially, when applied to 'chars', it can be used to express
nearness conditions. For example,
'"/*" quote "*/" in join(10,chars)'
selects comments "/* ... */" which are at most 10 characters
long.
EXAMPLES OF REGION EXPRESSIONS
Count the number of occurrences of string "sort" in file eval.c:
sgrep -c '"sort"' eval.c
Show all blocks delimited by braces in file eval.c:
sgrep '"{" .. "}"' eval.c
Show the outermost blocks that contain "sort" or "nest":
sgrep 'outer("{" .. "}" containing ("sort" or "nest"))'\
eval.c
Show all lines containing "sort" but no "nest" in files with an
extension .c, preceded by the name of the file:
sgrep -o "%f:%r" '"\n" _. "\n" containing "sort" \
not containing "nest"' *.c
(Notice that this query would omit the first line, since it has no
preceding new-line character '\n', and also the last one, if not
terminated by a new-line. For a correct way to express text lines, see
the definition of the LINE macro below.)
Show the beginning of conditional statements, consisting of "if"
followed by a condition in parentheses, in files *.c. The query has to
disregard "if"s appearing within comments "/* ... */" or on compiler
control lines beginning with '#':
sgrep '"if" not in ("/*" quote "*/" or ("\n#" .. "\n")) \
.. ("(" .. ")")' *.c
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Show the if-statements containing string "access" in their condition
part appearing in the main function of the program in source files
*.c:
sgrep '"if" not in ("/*" quote "*/" or ("\n#" .. "\n")) \
.. ("(" .. ")") containing "access" \
in ("main(" .. ("{" .. "}")) \
.. ("{" .. "}" or ";")' *.c
We see that complicated conditions can become rather illegible. The
use of carefully designed macros can make expressing queries much
easier. For example, one could give the below m4 macro processor
definitions in a file, say, c.macros:
define(BLOCK,( "{" .. "}" ))
define(COMMENT,( "/*" quote "*/" ))
changecom(%)
define(CTRLINE,( "#" in start or "\n#"
_. ("\n" or end) ))
define(IF_COND,( "if" not in (COMMENT or CTRLINE)
.. ("(" .. ")")))
Then the above query could be written more intuitively as
sgrep -p m4 -f c.macros -e 'IF_COND containing "access"\
in ( "main(" .. BLOCK ) .. (BLOCK or ";")' *.c
OPTIMIZATION
sgrep performs common subexpression elimination on the query
expression, so that recurring sub-expressions are evaluated only once.
For example, in expression
'(" " or "\n" or "\t") .. (" " or "\n" or "\t")'
the sub-expression
'(" " or "\n" or "\t")'
is evaluated only one.
DIAGNOSTICS
Exit status is 0 if any matching regions are found, 1 if none, 2 for
syntax errors or inaccessible files (even if matching regions were
found).
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ENVIRONMENT
One's own default options for sgrep can be given as a value of the
environment variable SGREPOPT. For example, executing
setenv SGREPOPT '-p m4 -o %r\n'
makes sgrep to apply m4 preprocessor to the expression and display
each output region as such followed by a line feed.
FILES
Sgrep tries to read the contents of the files $HOME/.sgreprc and
/usr/lib/sgreprc. Generally useful macro definitions may be placed in
these files. Using m4 (or some other) macro processor, for example
the following definitions could go in one of these files:
define(BLANK,( " " or "\t" or "\n"))
define(LEND,( "\n" or end ))
define(LINE,( start .. LEND or ("\n" _. LEND) ))
define(NUMERAL,( "1" or "2" or "3" or "4" or "5" or
"6" or "7" or "8" or "9" or "0" ))
FUTURE EXTENSIONS
+ Regular expressions (The most important missing feature)
+ Built-in macro preprocessor
+ More operations
+ Indexing for large static texts
AUTHORS
Jani Jaakkola and Pekka Kilpelainen, University of Helsinki,
Department of Computer Science, 1995.
BUGS
Sgrep may use lots of memory, when evaluating complex queries on big
files. When sgrep reads its input text from a pipe, it copies it to a
temporary file. sgrep does not have regular expressions in search
patters.
SEE ALSO
awk(1), ed(1), grep(1)
sgrep home page at http://www.cs.helsinki.fi/~jjaakkol/sgrep.html
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