Generate a histogram from a list of numbers

histogram.pl

#!/usr/bin/end perl

use strict;
use warnings;

use Data::Dumper;

my $hist = sub {
	my $input = shift;
	if ($input and $input =~ /^\d+$/) {
		my ($i, $j) = (1, 10);
		while ($j <= 1e9) {
			if ($input >= $i and $input < $j) {
				return $j;
			}
			else {
				$i *= 10;
				$j *= 10;
			}
		}
		return 1e9;
	}
	else {
		return 'junk';
	};
};

unless ($ARGV[0]) {
	print "usage: $0 <samples_file>\n";
	exit 0;
}
elsif (-f $ARGV[0]) {
	open(my $fh , '<', $ARGV[0]) or die "Unable to open file $ARGV[0]: $!";
	my %hg;
	while (<$fh>) {
		chomp;
		my $res = $hist->($_);
		print "$res\n";
		if ($hg{$res}) {
			$hg{$res}++;
		}
		else {
			$hg{$res} = 1;
		}
	}
	close $fh;
	print Dumper \%hg;
}