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Top Forums Shell Programming and Scripting Searching backwards using regular expressions Post 302389010 by drl on Friday 22nd of January 2010 06:48:36 AM
Old 01-22-2010
Hi.

I like utility cgrep for situations like this. It allows one to specify conveniently a regular expression for the previous and succeeding boundaries -- "windows":
Code:
#!/usr/bin/env bash

# @(#) s1	Demonstrate previous boundary match with cgrep.
# http://www.bell-labs.com/project/wwexptools/cgrep/

echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1)
set -o nounset
echo

FILE=${1-data1}

echo " Data file $FILE:"
cat $FILE

echo
echo " Results:"
cgrep -D -w "else if" "find me" $FILE

exit 0

producong:
Code:
% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0 
GNU bash 3.2.39

 Data file data1:
if(condition)
	multiline
	statement
else if(condition)
	multiline
	statement
else if(condition)
	multiline
	statement
else if(condition)
	multiline
	statement
else if(condition)
	multiline
	statement
	find me
else if(condition)
	multiline
	statement

 Results:
else if(condition)
	multiline
	statement
	find me

You will need to obtain, compile, and make available cgrep. See the URL mentioned in the script for that.

Best wishes ... cheers, drl
 

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regex(3)						     Library Functions Manual							  regex(3)

Name
       re_comp, re_exec - regular expression handler

Syntax
       char *re_comp(s)
       char *s;

       re_exec(s)
       char *s;

Description
       The  subroutine	compiles  a string into an internal form suitable for pattern matching.  The subroutine checks the argument string against
       the last string passed to

       The subroutine returns 0 if the string s was compiled successfully; otherwise a string containing an  error  message  is  returned.  If	is
       passed 0 or a null string, it returns without changing the currently compiled regular expression.

       The  subroutine returns 1 if the string s matches the last compiled regular expression, 0 if the string s failed to match the last compiled
       regular expression, and -1 if the compiled regular expression was invalid (indicating an internal error).

       The strings passed to both and may have trailing or embedded newline characters; they are terminated by	nulls.	 The  regular  expressions
       recognized are described in the manual entry for given the above difference.

Diagnostics
       The subroutine returns -1 for an internal error.

       The subroutine returns one of the following strings if an error occurs:

       No previous regular expression
       Regular expression too long
       unmatched (
       missing ]
       too many () pairs
       unmatched )

See Also
       ed(1), ex(1), egrep(1), fgrep(1), grep(1)

																	  regex(3)
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