caciqueman has asked for the wisdom of the Perl Monks concerning the following question:

I would like to reverse a string, and then un-reverse it so that another string can act on it (for substitution). Have searched the manuals with no luck. If I dont reverse it, but simply do this, it works: 
#!/usr/bin/perl
print "Content-type: text/html\n\n";

   ......This Works...................

$comment = "My lawyer is named will";

for ($new_comment = $comment) 
{
s/lawyer/Banker/eig; s/will/Barney/eig; s/is/Was/eig;
}
print $new_comment;

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But when I try to reverse the string or array, the results dont work on the first string, even if I call in inside a sub..... 


.......Why Doesnt This Work ? ................ 

$comment = "My lawyer is named will";

for ($new = $comment) {
$comment = &doit($comment);
}

sub doit{
$go = ";gie/moT/lliw/s ;gie/reknaB/reywal/s ;gie/yenraB/derf/s";
$com = join("", reverse split(//, $go));
return $com;
}
print $new;

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Yes, it is stupid to want to do this, but I need to. Could anyone please tell me how I might accomplish this. Thanks.

Edit kudra, 2002-04-15 Changed title

Replies are listed 'Best First'.
Re: newkid confused
by swiftone (Curate) on Apr 05, 2002 at 21:46 UTC
    Well, let's see what you're actually doing: 
    $comment = "My lawyer is named will";

   for ($new = $comment) {
   $comment = &doit($comment);
   }

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    Okay, this is probably not what you intend. This takes $new, and sets it equal to $comment. Then this is treated as a list (of 1 item), which is assigned to $_ in the for loop (the s// will by default work on $_), and then $comment is set equal to the result of doit(). 
       sub doit{
   $go = ";gie/moT/lliw/s ;gie/reknaB/reywal/s ;gie/yenraB/derf/s";

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    This sets $go equal to that string. 
       $com = join("", reverse split(//, $go));

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    This sets $com equal to the result of this. 
       return $com;
   }
   print $new;

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    which is then returned ($new being set equal to that).

    It seems you want to _run_ those searches against $new. You'll want an eval() statement to do that. (Why is left to your own twisted goals). I suggest you study the for() loop because I suspect you are misunderstanding what it is doing.

    Update: eval() can be a security risk if you are running anything that can be affected by user input, particularly on a web page. I suggest you use perl's taint mode, and CGI.pm

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      Here's a cleaned up version with some explanatory text. hope it helps, I have no idea why you would want to do this. 

      #!/usr/bin/perl -wT
#warnings and Taint checking on, see perlsec 

#CGI scripts should almost always use CGI.pm
use CGI;
use strict;  #strict is your friend

my $q = new CGI;
print $q->header();  #print the header

my $comment = "My lawyer is named will";

#this loops over the list in the parens, aliasing $new to each in turn
#pointless, but presumably you anticipate having more than one in the 
+list
for my $new ($comment) {
  $new = doit($new);  #We act on $new, which will affect whichever lis
+t element we're on
}
print $comment;  #$comment, not $new.  $new was only inside the loop


sub doit{
  my ($passed_string) =  @_;  #get the list we're passed, drop all but
+ first item
  #Note that I removed the "e" flags below, you aren't interpreting an
+ything
  my $go = ";gi/moT/lliw/s ;gi/reknaB/reywal/s ;gi/yenraB/derf/s";
  my $com = scalar reverse $go;
  $_ = $passed_string;  #so that s// will work on it.
  eval $com or die $!;
  return $_;
}

      [download]
      Update: Cleaned it up a bit, thanks to BazB and podmaster for the assist
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[d/l]
        Thanks ! The Reason: The string is actually lots longer. I have collected a Looonnnggg list of cusswords, in several languages, and the substitutions are for moronic language entered in a comments form. I would rather not show all the words to delicate people, if I ever run across any that is, so I like the s/'s backwards in the script. For example: 
        s/bit*h/barbie/
or s/wh*re/exwife/  etc.

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        I will study eval and the security problems.
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[d/l]
Re: newkid confused
by Zaxo (Archbishop) on Apr 05, 2002 at 21:53 UTC 
    my $foo = "My lawyer is named will";
my $oof = scalar reverse $foo;

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    You may find japhy's sexeger interesting.

    Update: Chady, it's a matter of self-documentation and of habit. By using explicit scalar() I say what I expect to happen, and with the habit of using it I can drop it into list context without concern. About the link, I'm delighted to have recommended it for a bowdlerware application.

    After Compline,
    Zaxo

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[d/l]

      I've been always using my $oof = reverse $foo; is there any particular reason for the scalar? isn't it already in a scalar context? will it break someday?

      He who asks will be a fool for five minutes, but he who doesn't ask will remain a fool for life.

      Chady | http://chady.net/
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[d/l]
        Your way is fine. Many people make it an explicit scalar reverse because it isn't always a scalar context. Take for example: 
        my $foo = "This is not a palindrome";
print reverse $foo;

        [download]
        print implies a list context, so reverse will take the list ($foo), and reverse it to ($foo) and print that result. Probably not what is intended. It also can take a while to debug, when the perfectly acceptable-looking reverse statement "doesn't work".

        Thus, if you get in the habit of being explicit about your context, you don't get caught.

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