Because the 0th element of @ARGV is empty and therefore uninitialized. To supress the warning just check if @ARGV has been populated e.g 
if(@ARGV and $ARGV[0] eq 'TEST') {
  print "$ARGV[0]\n";
}

[download]
See. perlvar for more info on @ARGV.
HTH

_________
broquaint

update: 'pritn' ne 'print', thanks to particle

In reply to Re: using $ARGV without arguments by broquaint
in thread using $ARGV without arguments by Anonymous Monk

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