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in reply to substitution in $0

I believe that I can provide an answer for why seek isn't happening how you would like it to. You are opening the file in append mode (with the ">>"). In this mode, anything you write will be appended to the original file. There is a lot of information gained by typing perldoc -f open at your nearest command prompt. And from what I see, I think that you need "+<" in front of the $0.

Enjoy.

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Re: Re: substitution in $0
by Helter (Chaplain) on Oct 02, 2002 at 13:40 UTC
    I agree, testing your code you need to either do as rollyguy has suggested, or it does work doing:
    open (PROG, "+>>$0");

    [download]
    In running your code withthe + in it, I have found your regexp does not work as well.
    Here is my version, and followed by the output: 

    #!/usr/bin/perl

use strict;
use warnings;

my $new_value = 10;
my $data=45;

open (PROG, "+>>$0");
seek (PROG, 0, 0);     #not working 
while (<PROG>)
{
  s/^(my .data\s*=\s*)\d+(\s*;)/$1.$new_value.$2/e;
  print;
}
close (PROG);

    [download]
    Output:
    #!/usr/bin/perl

use strict;
use warnings;

my $new_value = 10;
my $data=10;

open (PROG, "+>>$0");
seek (PROG, 0, 0);     #not working 
while (<PROG>)
{
  s/^(my .data\s*=\s*)\d+(\s*;)/$1.$new_value.$2/e;
  print;
}
close (PROG);

    [download]

    Note: I'm not writing to the file itself, now that I'm thinking about it you probably want to write a temp file, then copy it over....

    Hope this helps!
[reply]
[d/l]
[select]
      Thanks to all you monks for the precious suggestions you gave to me!
      I know my code is still terrible!! 
      #!perl

use strict;
use warnings;

&changemyself();
sub changemyself{
  my $new_value = 10;
  my $data=6666666666666;   #next time this value will be 10

 open (COPIA, ">copia");
 open (PROG, "+>>$0");
 seek (PROG, 0, 0);         #I don't know why but it's NECESSARY!

 while (<PROG>)
 {
   s/^(  my .data\s*=\s*)\d+(\s*;)/$1.$new_value.$2/e;
   print COPIA;
 }
 close (PROG);              #
 close (COPIA);             #
                            #   the terrible imitation 
                            #     of the
 open (COPIA, "<copia");    #   three cards game
 open (PROG, ">$0");        #
 while (<COPIA>){print PROG}#
 close (PROG);              #
 close (COPIA);             #
 unlink ("copia");          #
}

      [download]
      Special thank to Helter!
      greetings from roma, lor*
      PS I never noticed the +>> operator!!! l*
[reply]
[d/l]
         open (PROG, "+>>$0");
 seek (PROG, 0, 0);   #I don't know why but it's NECESSARY!

        [download]

        Because  >> moves the file position to end-of-file.

[reply]
[d/l]
[select]

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