find a substring using regex and then replace it

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

Dear Monks,

I want to achieve following. I have a string called bge1 and I want to convert it to bge:1. to make it more specific, search the substring in the end of string and if it is number replace it with :number. I am trying following

my $Interface = bge1;
$Interface =~ s/[0-9]\$/:\$&/;
[download]

but still result is bge1

what is wrong with it?

Comment on find a substring using regex and then replace it Download Code

Replies are listed 'Best First'.
Re: find a substring using regex and then replace it by toolic (Bishop) on May 02, 2016 at 14:21 UTC
You should not escape the $'s: `use warnings; use strict; my $Interface = 'bge1'; $Interface =~ s/[0-9]$/:$&/; print "$Interface\n"; __END__ bge:1` [download] Unrelated to your problem, but... Tip #1 from the Basic debugging checklist: use strict and warnings Also, consider using `$Interface =~ s/([0-9])$/:$1/;` to avoid performance issues.	[reply] [d/l] [select]
Re: find a substring using regex and then replace it by hippo (Archbishop) on May 02, 2016 at 14:24 UTC
There are 2 problems there: you are using bge1 as a bareword and you are escaping the dollars in the regex thus preventing them from doing what you want. Here's the working version: `#!/usr/bin/env perl use strict; use warnings; my $Interface = 'bge1'; $Interface =~ s/[0-9]$/:$&/; print $Interface . "\n";` [download] which outputs "bge:1".	[reply] [d/l]
Re^2: find a substring using regex and then replace it by johngg (Canon) on May 02, 2016 at 16:08 UTC
It's unlikely but not beyond the realms of possibility to have more than ten interfaces so it would be safer to match for one or more (`+`) digits at the end of the string. This gives the wrong result:- `$ perl -Mstrict -Mwarnings -E ' my $interface = q{bge12}; $interface =~ s{[0-9]$}{:$&}; say $interface;' bge1:2 $` [download] This corrects the problem. I also prefer to use the `\d` special escape for digits and a look-ahead to save having to mention what was matched in the replacement part:- `$ perl -Mstrict -Mwarnings -E ' my $interface = q{bge12}; $interface =~ s{(?=\d+$)}{:}; say $interface;' bge:12 $` [download] I hope this is of interest. Cheers, JohnGG	[reply] [d/l] [select]