use warnings;
use strict;

my $dirname = $ARGV[0] // '.';

for ( glob("$dirname/*") ) {
    if ( !-d ) {
        read_file($_);
    }
}

sub read_file {
    my $filename = shift;

    open my $fh, '<', $filename or die "can't open file:$! ";
    while (<$fh>) {
        print $_ if $. == 10;
    }
}