topic Re: Help Regarding Perl Regular Expression(Pattern Matching) in Operating System - Linux

Help Regarding Perl Regular Expression(Pattern Matching)

Pankaj Yadav_1 — Sat, 16 Sep 2006 05:36:42 GMT

The expression is -->

if($x =~ /$y/g) {
#where $x=41 and $y=424143

Please tell me if the above expression will work ?
If not then how to match $x and $y ?

Re: Help Regarding Perl Regular Expression(Pattern Matching)

James R. Ferguson — Sat, 16 Sep 2006 11:19:14 GMT

HI:

If you are looking to see if the character string "41" held in $x exists in $y (anywhere) then:

# perl -le '$x=41;$y=424143;if ($y =~ /$x/g) {print "ok"}'

...will print "ok".

Regards!

...JRF...

Re: Help Regarding Perl Regular Expression(Pattern Matching)

James R. Ferguson — Sat, 16 Sep 2006 11:32:49 GMT

Hi (again):

An excellent tour and summmary of Perl regular expression syntax, can be found here:

http://perldoc.perl.org/perlre.html

At it's end are additional references, including Jeffrey Friedl's "Mastering Regulare Expressions" --- an outstanding book on the subject.

Regards!

...JRF...

Re: Help Regarding Perl Regular Expression(Pattern Matching)

Hein van den Heuvel — Sat, 16 Sep 2006 11:40:21 GMT

Just to see whether a simple (non-wildcard) string is a substring of an other string you should NOT use a regular expression.

Instead, use the 'index' function which is made specifically for that and processes more efficiently:

Same example:
perl -le '$x=41;$y=424143;if (index($y,$x) >= 0 ) {print "ok"}'

(one of many) Online documentation:
#http://www.xav.com/perl/lib/Pod/perlfunc.html#item_index

hth,
Hein van den Heuvel
HvdH Performance Consulting

Re: Help Regarding Perl Regular Expression(Pattern Matching)

H.Merijn Brand (procura — Sun, 17 Sep 2006 04:11:48 GMT

And if that is the only thing and the only time you match that/a pattern in the target string, PLEASE drop the /g modifier, as it has many side effects.
The /g modifier is for global matches, and returns more matches if available, changing the context if needed. It also fiddles with global variables and string attributes, so you can match on from the last position with \G metacharacters. The /g modifier is related to the /c modifier.

# perldoc perlretut

About 52% or 1188 lines down is the explanation of /g and /c

Enjoy, Have FUN! H.Merijn

Re: Help Regarding Perl Regular Expression(Pattern Matching)

Pankaj Yadav_1 — Tue, 19 Sep 2006 06:30:57 GMT

I got the solution by
perl -le '$x=41;$y=424143;if (index($y,$x) >= 0 ) {print "ok"}'

which is suggested by Hein van Den.

Thanks a lot to all of you.