sub Which($)
  {
   my $Filename=shift;
   my @Arr = ( split /\:/,$ENV{PATH} )
   for(my $i = 0; $i <= #$Arr; $i += 2)
   {
    return "$Arr[$i]/$Filename\n" if ( -e "$Arr[$i]/$Filename" );
    return "$Arr[$i+1]/$Filename\n" if ( -e "$Arr[$i+1]/$Filename" );
   };
  }