Zigzag Cypher

The Zigzag cypher (also known as a Rail Fence is a simple transposition scheme and not very strong, this is just an exercise in tinkering.
First here is the encoder:

#!/usr/bin/perl
 $rowlen = @ARGV[0];
 $message = @ARGV[1];
 if ( @ARGV == 0) {
   $message="CHARLIETHEWONDERBUDGIE";
   $rowlen =6;
 }
 $rowlen -- ;
 @letter = split '', $message;
 
 $dir =0;
 $index =0 ;

for ($r=0;$r<= @letter ;$r++){  
 @array[$index]=@array[$index].@letter[$r];  
 if($dir == 0) { $index++; } 
 if($dir == 1) { $index--; } 
  if ($index >$rowlen ) {
   $dir = 1 ;
   $index-=2;
  }
 if ($index <0) {
  $dir=0; 
  $index+=2;
 }
}

for ($r=0;$r<= $rowlen ;$r++){  
print @array[$r]   ;
}
print "\n";

After some trial and error the decoder

#!/usr/bin/perl

sub unzig {
#adjust for zero-numbering 
 $rowlen--  ;
 @letter= split '', $cryptStr;
 
 for ($r=0;$r <= scalar(@letter) ;$r++){  
  @array[$r]=" ";
 }

$rowIndex =0;
$tempIndex=0;
$arrayLen = @letter-1;
$r=0;
$newrow=0;
while($r <= $arrayLen ){  
 if ($newrow == 1 ) { 
# new row
  $rowIndex++;
  $tempIndex = $rowIndex;
  @array[$tempIndex] = @letter[$r]; 
  if ($rowIndex == $rowlen) { 
    $tempIndex = $tempIndex+2*$rowlen;
  } else { 
    $tempIndex = $tempIndex+(2*($rowlen-$rowIndex));
  } 
  $r++;
  $newrow=0;
 } else {

   if(($rowIndex > 0 ) ) { #don't do on first row
     if($newrow==0) {
       @array[$tempIndex] = @letter[$r]; 
       $r++;
       $tempIndex = $tempIndex+2*$rowlen-(2*($rowlen-$rowIndex));
       if ($tempIndex >$arrayLen) { $newrow =1; }
     } 
   }

   if($rowIndex != $rowlen) { #don't do on last row
     if($newrow==0){ 
       @array[$tempIndex] = @letter[$r];
       $r++; 
       $tempIndex = $tempIndex+(2*($rowlen-$rowIndex));
       if ($tempIndex > $arrayLen) { $newrow =1 ; }
     }
   }
 }
}

for ($r=0;$r <= scalar(@letter) ;$r++){  
 print @array[$r];
}

print "\n";
} #end sub

#main
 $rowlen = @ARGV[0];
 $cryptStr = @ARGV[1];
 if ( @ARGV == 0) {
  print "call with ./zigzag_d.pl rowlength cryptmessage \neg. ./zigzag_d.pl 3 COPATGAHRRY\n";
  #do a demo 
  $cryptStr="WECRLTEERDSOEEFEAOCAIVDEN";
  $rowlen =3;
  unzig;
 } else {
  #there was command line input 
  unzig;
}

And a few lines for a test script

./zigzag_e.pl 3 CARTOGRAPHY
./zigzag_d.pl 3 COPATGAHRRY

./zigzag_e.pl 4 THISISENCRYPTEDWITHTHEZIGZAGCYPHER
./zigzag_d.pl 4 TETHGPHSNPETTIZYHIICYDIHZACESRWEGR

./zigzag_d.pl 6 CWIHEOGEAHNDRTDULEEBIR
./zigzag_d.pl 10 CERHDYTOHEGASSVAOOEFCLWADANR