Why a regexp won't increment the value of a variable

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hello Perlmonks,

This might sound a really stupid question, but I have been playing with this for a while and I still don't get the result I am expecting.

I want to read a file line by line and when a certain pattern is matched want to substitute that pattern for something like "$replacement-$counter" where $replacement never changes on the script and $counter comes from a for loop. Basically I have a template that I want to use many times.

Here is my code, I put in red where I hit the problem:

#!/usr/bin/perl

use Getopt::Long;
use strict;

my $template;
my $replacement;
my $prefix;
my $total;
my $counter;
my @template;

GetOptions (
    "template=s"    => \$template,
    "replacement=s" => \$replacement,
    "prefix=s"      => \$prefix,
    "total=i"       => \$total,
    );

open FH, "< $template" or die "Couldn't open the file $template\n";
@template = <FH>;
close FH;
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for ($counter=0; $counter<$total; $counter++) {
    foreach (@template) {
        $_ =~ s/$replacement/${prefix}-${counter}/;
        print $_;
    }
}
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My Template file looks like this:

enable config protocol mpls lsp name __replaceme__
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And I always get the initial value of $counter in the replacement like this:

# ./create_rsvp_lsp.pl -template lsp_template.tpl -replacement "__name
+__" -prefix "lsp_to_1.1.118.152" -total 5
enable config protocol mpls lsp name lsp_to_1.1.118.152-0
enable config protocol mpls lsp name lsp_to_1.1.118.152-0
enable config protocol mpls lsp name lsp_to_1.1.118.152-0
enable config protocol mpls lsp name lsp_to_1.1.118.152-0
enable config protocol mpls lsp name lsp_to_1.1.118.152-0
[download]

What am I doing wrong here?

Many thanks!

Comment on Why a regexp won't increment the value of a variable Select or Download Code

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Re: Why a regexp won't increment the value of a variable by almut (Canon) on Nov 24, 2008 at 20:24 UTC
Looks like you're modifying `@template` on the first iteration (remember that `$_` in the `foreach` loop is an alias), so the replacement string is no longer found in the subsequent iterations...	[reply] [d/l] [select]
Re: Why a regexp won't increment the value of a variable by gmoque (Acolyte) on Nov 24, 2008 at 20:50 UTC
Thanks almut, You are right, I forgot that on the first time $_ contains the original value so in the next iterations there is no match at all, I created the local var in the loop so I never change my template: `for ($counter=0; $counter<$total; $counter++) { foreach (@template) { my $line = $_; $line =~ s/$replacement/${prefix}-${counter}/; print $line; } }` [download] JavaFan, I don't think that was what I needed but thanks!	[reply] [d/l]
Re: Why a regexp won't increment the value of a variable by Anonymous Monk on Nov 24, 2008 at 20:19 UTC
Sorry I wrote the wrong command, this is the good one: `# ./create_rsvp_lsp.pl -template lsp_template.tpl -replacement "__repl +aceme__" -prefix "lsp_to_1.1.118.152" -total 5` [download]	[reply] [d/l]
Re: Why a regexp won't increment the value of a variable by JavaFan (Canon) on Nov 24, 2008 at 20:40 UTC
Perhaps you want something like: `my $counter = 0; foreach (@template) { $counter++ if s/$replacement/${prefix}-${counter}/; print; }` [download]	[reply] [d/l]