Hello atcroft,

The only way I can find to do this is to pull the substitution apart into its component steps and perform these separately:

#! perl
use strict;
use warnings;

my $c = q{asdfghjk};

my @regex =
(
    { lh => q{(gh)}, rh => q{__$1__}, }, 
    { lh => q{(h_)}, rh => q{_h!$1!}, }, 
);

print q{Original: }, $c, "\n";

for my $i (0 .. $#regex)
{
    if ($c =~ /$regex[$i]{lh}/)
    {
        my $s =  $1;
        my $d =  $regex[$i]{rh};
           $d =~ s/\$1/$s/;
           $c =~ s/$regex[$i]{lh}/$d/;
    }
}

print q{Final: }, $c, "\n";
[download]

Output:

17:37 >perl 1352_SoPW.pl
Original: asdfghjk
Final: asdf__g_h!h_!_jk

17:39 >
[download]

This is far from elegant, and I keep thinking there must be a simpler way involving s///ee — but I haven’t found it.

Anyway, hope that helps,