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get the matching regex pattern Ram Prasad 03-20-2008
Posted by Ram Prasad on March 20, 2008, 9:16 am
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 I have a somewhat strange requirement
I want to find if a regex matched what exactly matched

to reproduce this

------------------
my @x;
$x[0] = 'chi+ld*';
$x[1] = '\sjoke';

$_=getinput(); # for test assume $_="This is a joke";

if(/($x[0]|$x[1])/){
print "Matched '$1' \n";
}
-----------------


I want to know if $x[0] matched or $x[1] matched
What is the most efficient way of doing this ?


Thanks
Ram



--
For spammers only
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Posted by comp.llang.perl.moderated on March 20, 2008, 12:36 pm
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> I have a somewhat strange requirement
> I want to find if a regex matched what exactly matched
>
> to reproduce this
>
> ------------------
> my @x;
> $x[0] = 'chi+ld*';
> $x[1] = '\sjoke';
>
> $_=getinput(); # for test assume $_="This is a joke";
>
> if(/($x[0]|$x[1])/){
> print "Matched '$1' \n";}
>
> -----------------
>
> I want to know if $x[0] matched or $x[1] matched
> What is the most efficient way of doing this ?
>

One way:

if ( / ($x[0]) | ($x[1]) /x ) {
print defined $1 ? "first" : "second";
}

But, this may be more efficient often:

if ( /$x[0]/ ) { print "first" }
elsif ( /$x[1]/) { print "second" }

Ordering alternatives with the most likely
matches in front can greatly increase efficiency
too.

--
Charles DeRykus

Posted by Jim Gibson on March 20, 2008, 1:06 pm
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In article

> I have a somewhat strange requirement
> I want to find if a regex matched what exactly matched
>
> to reproduce this
>
> ------------------
> my @x;
> $x[0] = 'chi+ld*';
> $x[1] = '\sjoke';
>
> $_=getinput(); # for test assume $_="This is a joke";

Then why not do us a favor and replace the above line with:

$_ = "This is a joke";

>
> if(/($x[0]|$x[1])/){
> print "Matched '$1' \n";
> }
> -----------------
>
>
> I want to know if $x[0] matched or $x[1] matched
> What is the most efficient way of doing this ?

One way is to capture the individual alternatives and test the
corresponding dollar values:

#!/usr/local/bin/perl
use strict;
use warnings;

my @x;
$x[0] = 'chi+ld*';
$x[1] = '\sjoke';

try("This is a joke");
try("Save the children");

sub try
{
$_ = shift;
if(/(($x[0])|($x[1]))/){
print "Matched '$1' \n";
print "\$2=$2\n" if $2;
print "\$3=$3\n" if $3;
}
}

Output:

Matched ' joke'
$3= joke
Matched 'child'
$2=child

This will not scale very well for many alternatives. For that, you can
inspect the @- array after the match.

--
Jim Gibson

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Posted by Gunnar Hjalmarsson on March 20, 2008, 1:44 pm
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Ram Prasad wrote:
> I have a somewhat strange requirement
> ...

You had posted the same question to the beginners mailing list just a
few minutes before you posted here, and I just spent a few minutes
answering the question there without knowing that you already had been
helped here.

DO NEVER DO THAT AGAIN !!!

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

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