Re^4: regex question

if you capture something by () in regex and you get $1,$2,$3 and so on, why can't you just do

s/$2/something/
[download]

In this script, it's doing it but it's changing the value rather than position. What i mean is,


[root@myserver tmp]# cat perl.test
#!/usr/bin/perl -w

use strict;

my $string = "123 123 345";
if ("$string" =~ /(\d+)\s+(\d+)\s+(\d+)/) {
    $string =~ s/$2/something/;
    print "$string\n";
}

[root@myserver tmp]# ./!$
./perl.test
something 123 345
[download]

I wanted this to change the value of position $2, Therefore wanted to see
123 something 345

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Re^5: regex question by johngg (Canon) on Nov 12, 2007 at 19:21 UTC
That happens because your second capture, held in `$2`, is "123" so in your substitution inside the `if` `$2` is interpolated to give `s/123/something/`, which runs quite happily and replaces the first occurence of "123" in `$string`. Had your string been "987 123 345" your code would have given the result you wanted but only as a side effect of your error. You could do it like this (not tested) `use strict; use warnings; my $string = q{123 123 345}; if ( $string =~ s{^(\d+\s+)(?:\d+)(\s+\d+)}{$1something$2} ) { print qq{Succeeded\n$string\n}; } else { print qq{Failed\n$string\n}; }` [download] I hope this makes things a bit clearer. Cheers, JohnGG	[reply] [d/l] [select]

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Re^5: regex question
by johngg (Canon) on Nov 12, 2007 at 19:21 UTC

$2

if

$2

s/123/something/

$string

use strict;
use warnings;

my $string = q{123 123 345};
if ( $string =~ 
     s{^(\d+\s+)(?:\d+)(\s+\d+)}{$1something$2} )
{
    print qq{Succeeded\n$string\n};
}
else
{
    print qq{Failed\n$string\n};
}
[download]

I hope this makes things a bit clearer.

Cheers,

JohnGG

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