gistfile1.pl

#!/usr/bin/env perl
use strict;
use warnings;
use File::Modified;
use Perl6::Say;

my ($command, @files) = @ARGV;

my $watcher = File::Modified->new(
    method => 'mtime',
    files  => \@files,
);

while(1) {
    my @changes;
    eval { @changes = $watcher->changed };
    say STDERR "$_ is changed." for @changes;
    if (@changes) {
        $watcher->update;
        system($command);
    }
    sleep 1;
}