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Full Discussion: The asterisk in regex
Top Forums UNIX for Dummies Questions & Answers The asterisk in regex Post 302649047 by Corona688 on Wednesday 30th of May 2012 05:52:31 PM
Old 05-30-2012
Quote:
Originally Posted by sudon't
I know through (my very limited) experience that you can't use the asterisk alone in a regex, but I still don't quite understand why. After all, it should match 'any or no characters'.
Zero or more what, is the question. * is a modifier that changes the character before it. You may be used to globs, where * exists by itself and needs no specifier in front of it because it always matches everything. Regexes are not that.

. is a special character that means "anything".

"A*" on the other hand would match "", "A", "AA", "AAAAAAAAAA" and so forth.

"[0-9]*" would match "0123", etc.
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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. ATTRIBUTES
Multithreading (see pthreads(7)) The re_comp() and re_exec() functions are not thread-safe. 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 3.53 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
2013-06-21 RE_COMP(3)
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