You can separate a variable name from following alphanumerics using curly brackets, a la: 

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

$_ = q{some search criteria};
s/(s)(o)(m)(e)( )search criteria/$1$2${3}2010$4$5/g;
print;

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See Regexp Quote Like Operators for details on regular expression interpolation.

In reply to Re: backreference followed by literal in regex substitution by kennethk
in thread backreference followed by literal in regex substitution by jayw

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