#!/usr/bin/perl

use strict;
use warnings;

my $Usage = "Usage: $0  [-p path/to/search]   regex\n";
if ( @ARGV > 2 and $ARGV[0] eq '-p' ) {
    shift;
    chdir $ARGV[0] or die "Can't chdir to $ARGV[0]: $!\n";
    shift;
}
die $Usage unless ( @ARGV == 1 );

my $regex = shift;

opendir( D, '.' );
my @files = grep { -f } readdir D;  # we only want to look at data files
my @matches;

for my $f ( @files ) {
    open( F, $f ) or do {
        warn "open failed for $f: $!\n";
        next;
    };
    while (<F>) {
        if ( m{$regex} ) {
            push @matches, $f;
            last;
        }
    }
}

print "The pattern {$regex} was found in ", scalar @matches, " files:\n";
print "@matches\n";