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Top Forums UNIX for Dummies Questions & Answers Help | Unix | grep | regular expression | backreference | Syntax/Logic Post 302361471 by MykC on Tuesday 13th of October 2009 09:26:14 AM
Old 10-13-2009
Ok, so if I'm trying to use grep to execute the regular expression:

Code:
^(.*)(\r?\n\1)+$

To remove duplicate lines that are in sequence, then its simply a regular expression that goes beyond what grep is able to execute/interpret because it can't deal with more than one line at a time. Ok, I read a bit about the concept about line boundaries and it seems this one of the things sed is used for.

Code:
ps -e | grep -o "[^ ]*$" | sort -u

Is what I used to get the output I was trying to achieve, but this more of an experiment with grep rather getting the output. I guess I going to have to familiarize myself with the concept of line boundaries and any tricks I can use to work with them in odd ways.

Finally, I'm going to play around with this a bit but if grep can't remove duplicate lines like uniq it might be able to remove duplicate characters or patterns.

Last edited by MykC; 10-13-2009 at 10:56 AM..
 

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REGEX(3)						     Library Functions Manual							  REGEX(3)

NAME
re_comp, re_exec - regular expression handler SYNOPSIS
char *re_comp(s) char *s; re_exec(s) char *s; DESCRIPTION
Re_comp compiles a string into an internal form suitable for pattern matching. Re_exec checks the argument string against the last string passed to re_comp. Re_comp returns 0 if the string s was compiled successfully; otherwise a string containing an error message is returned. If re_comp is passed 0 or a null string, it returns without changing the currently compiled regular expression. Re_exec 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 re_comp and re_exec may have trailing or embedded newline characters; they are terminated by nulls. The regular expressions recognized are described in the manual entry for ed(1), given the above difference. SEE ALSO
ed(1), ex(1), egrep(1), fgrep(1), grep(1) DIAGNOSTICS
Re_exec returns -1 for an internal error. Re_comp returns one of the following strings if an error occurs: No previous regular expression, Regular expression too long, unmatched (, missing ], too many () pairs, unmatched ). 3rd Berkeley Distribution May 15, 1985 REGEX(3)
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