Perl:string substitution Pattern: ='abc...', Post: 302279082

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Top Forums Shell Programming and Scripting Perl:string substitution Pattern: ='abc...', Post 302279082 by KevinADC on Thursday 22nd of January 2009 12:58:35 AM

01-22-2009

Registered User

Quote:

Originally Posted by Niroj

o/p=> c1: c2: c3:

Thanks Kelvin ! But could plz explain How does it work for c3='hg5 sh'.
(c3='.....' does not end with a comma "," !!)?

In the regexp you see ,?. In this context the ? symbol is a quantifier that means zero or one of whatever is to the left of it. So it will match zero or one comma.

Quote:

Originally Posted by Niroj

And my 2nd query is why "$str =~ s/='.*',?/:/g;" gives o/p as "c:" , though it should stop at c2='...', bcoz c3='..' doesn't end with a comma..

In your regexp you have used .* which means to match zero or more of anything as much as possible. This is called greedy matching. So it matches whatever is between the first single quote and the last single quote in the string. What you should have done was used .*? which means to match zero or more of anything but as little as possible. This is called stingy matching. But using the negated character class [^'] is actually more efficient then using .*? to achieve the same result.

KevinADC

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tcl_stringmatch

Tcl_StringMatch(3)					      Tcl Library Procedures						Tcl_StringMatch(3)

__________________________________________________________________________________________________________________________________________________

NAME

       Tcl_StringMatch, Tcl_StringCaseMatch - test whether a string matches a pattern

SYNOPSIS

       #include <tcl.h>

       int
       Tcl_StringMatch(str, pattern)

       int
       Tcl_StringCaseMatch(str, pattern, flags)

ARGUMENTS

       const char *str (in)		 String to test.

       const char *pattern (in) 	 Pattern to match against string.  May contain special characters from the set *?[].

       int flags (in)			 OR-ed combination of match flags, currently only TCL_MATCH_NOCASE.  0 specifies a case-sensitive search.
_________________________________________________________________

DESCRIPTION

       This  utility  procedure  determines  whether  a  string  matches  a given pattern.  If it does, then Tcl_StringMatch returns 1.  Otherwise
       Tcl_StringMatch returns 0.  The algorithm used for matching is the same algorithm used in the string match Tcl command and  is  similar	to
       the algorithm used by the C-shell for file name matching;  see the Tcl manual entry for details.

       In  Tcl_StringCaseMatch,  the algorithm is the same, but you have the option to make the matching case-insensitive.  If you choose this (by
       passing TCL_MATCH_NOCASE), then the string and pattern are essentially matched in the lower case.

KEYWORDS

       match, pattern, string

Tcl									8.5							Tcl_StringMatch(3)

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