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

In reply to Re^2: find a substring using regex and then replace it by johngg
in thread find a substring using regex and then replace it by swissknife

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