In case you have Term::ReadLine::Gnu installed, you can do:

#!/usr/bin/perl

use Term::ReadLine;

my $term = new Term::ReadLine 'Demo';

my $prompt = '$\\HEAD\\';
my $dir    = "foo/bar";  # user-editable default input

my $user_input = $term->readline($prompt, $dir);
print "user_input: $user_input\n";
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(BTW, what you refer to as STDIN is usually called the terminal/console's prompt, strictly speaking...)