#!/usr/bin/perl -w
use strict;

my $str  = 'abcadefaghi';
my $pat  = '(a.)';
my $repl = '\u$1 ';

$str =~ s/$pat/
         my @save = (undef, $1, $2, $3, $4, $5, $6);
         $repl =~ s{\$$_}{$save[$_]}g for 1..6;
         $repl;
        /eg;

print "$str\n";