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

my $path = '/Users/Maxi/Desktop/Verzeichnis beispiel';

opendir my $DIR, $path or die " the directory couldn't be opened\n";

my @folder = grep -f "$path/$_", readdir $DIR;

for my $file (@folder) {
    open my $FIL ,'<', "$path/$file" or die "the file $file couldn't be opened: $!\n";
    while (<$FIL>) {
        print if /perl/i;
    }
}