while (<*>) {
    $o = $_;
    s/\ /\¬/g;
    rename( $o, $_ ) or die "rename $o to $_: $!";
}
foreach (<*.avi>) {
    $cmd = "mkvmerge $_ -o ";
    s/\.avi$/.mkv/;
    $cmd .= $_;
    print "$cmd\n";
    system($cmd) == 0 or die "$cmd: failed with status $?";
}

##</code><code>##

use strict;
use warnings;