grep -il "^$input" *

##</code><code>##

perl -lne '$seen{$ARGV} = 1 if /^'"$input/i }{ print for keys %seen" *

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

my $input = shift;
for my $file (glob '*') {
    open my $IN, '<', $file or die $!;
    while (<$IN>) {
        if (/^$input/i) {
            print "$file\n";
            last;
        }
    }
}