my $aha = 'upon';
my $oho = 'a';
my $text = 'once $aha $oho time';
$text =~ s/\$(\w+)/${$1}/g;
print $text;
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If you have variable names containing something other than just \w, you'll have to expand the regex a bit, but there's the mechanism you need. ${'varnam'} is the same as $varname.