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Top Forums Shell Programming and Scripting why "aab" matchs "ab" when using reglar expression ? Post 302549077 by 915086731 on Sunday 21st of August 2011 08:40:35 AM
Old 08-21-2011
why "aab" matchs "ab" when using reglar expression ?

Please see the following code, why "aab" matchs "ab" when using reglar expression ?
Code:
[saturn@saturn-pc new]$ [[ "aab" =~ "ab" ]] && echo "ok" || echo "error";
ok                                   
[saturn@saturn-pc new]$ [[ "aab" =~ "a*b" ]] && echo "ok" || echo "error";
error                          
[saturn@saturn-pc new]$ [[ "aab" =~ "a.b" ]] && echo "ok" || echo "error";
error            
[saturn@saturn-pc new]$ [[ "aab" =~ "aab" ]] && echo "ok" || echo "error";
ok
[saturn@saturn-pc new]$

Thanks!
 

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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(const char *regex); int re_exec(const 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
For an explanation of the terms used in this section, see attributes(7). +---------------------+---------------+-----------+ |Interface | Attribute | Value | +---------------------+---------------+-----------+ |re_comp(), re_exec() | Thread safety | MT-Unsafe | +---------------------+---------------+-----------+ 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 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. GNU
2017-09-15 RE_COMP(3)
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