if( $#ARGV==0  || !$ARGV[0] || !grep{ $ARGV[0] eq $_,}@arr ) {
...

# Die Usage
if(($#ARGV==0) || (! $ARGV[0]) || (grep{ $ARGV[0] eq $_,} @array )) {
        print "\nUsage: $0 <argument>\n\n";
        print "argument: \n";
        print '-'x20 . "\n";
        foreach (@array){print "$_\n";}
        exit 1;
}

if(($#ARGV==0) || (!grep{ $ARGV[0] eq $_} @array )) {
..

if(($#ARGV==-1) || (!grep{ $ARGV[0] eq $_ } @array ? print $_, "Vorhanden\n" : print $_, "Nicht vorhanden!\n")) {
...

Use of uninitialized value in print at skript.pl line 12.
Vorhanden

Usage...