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I have tried everything I can think of and cannot solve this. Any help appreciated.

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

my ($s, $pat, $rpl);

$s = "ABCDEF abc000 RSTUV";
$pat = '(.*abc)...(.*)';
$rpl = '${1}777${2}';

# Works...
$_ = $s;
s/(.*abc)...(.*)/${1}777${2}/;
print "$_\n";

# Does not work...
$_ = $s;
s/$pat/$rpl/;
print "$_\n";

OUTPUT:
ABCDEF abc777 RSTUV
${1}777${2}

s/$pat/eval qq("$rpl")/e;