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Top Forums Shell Programming and Scripting help for fast way of finding line number for a regex Post 302552667 by pludi on Monday 5th of September 2011 05:29:07 AM
Old 09-05-2011
Of course it's slow, what you're doing is akin to trying to repairing a watch using a hammer: it's possible, but frustrating. In this case, the regex as you're applying it has to scan each line completely, checking each character on each line, checking for a match.

So the first question is: is it really a regex, or is it a fixed string?
And the second: can the regex be anchored in some way? Eg, start of the line, or the only word on the line, or something else to minimize the search cost?
 

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RE_COMP(3)						     Linux Programmer's Manual							RE_COMP(3)

NAME
re_comp, re_exec - BSD regex functions SYNOPSIS
#define _REGEX_RE_COMP #include <sys/types.h> #include <regex.h> char *re_comp(char *regex); int re_exec(char *string); DESCRIPTION
re_comp() is used to compile the null-terminated regular expression pointed to by regex. The compiled pattern occupies a static area, the pattern buffer, which is overwritten by subsequent use of re_comp(). If regex is NULL, no operation is performed and the pattern buffer's contents are not altered. re_exec() is used to assess whether the null-terminated string pointed to by string matches the previously compiled regex. RETURN VALUE
re_comp() returns NULL on successful compilation of regex otherwise it returns a pointer to an appropriate error message. re_exec() returns 1 for a successful match, zero for failure. CONFORMING TO
4.3BSD. NOTES
These functions are obsolete; the functions documented in regcomp(3) should be used instead. SEE ALSO
regcomp(3), regex(7), GNU regex manual COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
1995-07-14 RE_COMP(3)
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