It appears from the problem description that the keys are all three characters, but just as a heads-up, you might want to add a reverse to that:
my $match = '('.join('|', reverse sort keys %replace).')';
The reverse ensures that the longest match is found even if some pattern is a prefix of another (which, in my experience, is generally the desired outcome). e.g.:
#!/usr/bin/perl -l
use strict;
use warnings;
my %replace = qw/pre 1 prefix 2/;
my $norev = '('.join('|', sort keys %replace).')';
my $withrev = '('.join('|', reverse sort keys %replace).')';
while (<DATA>) {
chomp;
print "Line: $_";
print "norev <$1>" if /$norev/;
print "w/rev <$1>" if /$withrev/;
}
__END__
This line contains prefix (which also matches 'pre')
Should print:
Line: This line contains prefix (which also matches 'pre')
norev <pre>
w/rev <prefix>
|