Try this and see how you get on. Note the comments.

#!perl     #Adjust for your system
use warnings;
use strict; # You did just forget these 2 lines?

my $lcount=0;        # Of course you'll need to declare your variables
+ with my
my $userout='';
my $listfile = "your filename";

# Always check that the open worked.
open(FILE, $listfile) or die "Couldn't open $listfile: $!\n";

while(my $user = <FILE>) {

#    $user =~ s/(\r|\n)//; # windows compatibility 
    chomp $user; # Does what you were trying to do above but works on 
+Macs as well

    $userout .= $user . ','; # Does the same.
    $lcount++;
    if ($lcount == 20) {
        print PIPE $userout; # no need to interpolate vars to print th
+em

        # I assume this means you want to print them to ALL to PIPE 20
+ at a time
        $lcount=0;    

        # In which case you need to clear $userout
        $userout = '';

        #If you only want the first 20 uncomment the next line 
        # last;
    }
#    next if !$user;    #No idea what you thought this did?
}
[download]

  chomp($user);
[download]

Just an additional note on that - while your regex is better written as chomp($user) you can make an improvement by using a character class instead of alternation:

You wrote $user =~ s/(\r|\n)//.

You *meant* $user =~ s/(\r|\n)$// since that newline should only occur at the end of the string.

That group is capturing but it doesn't need to $user =~ s/(?:\r|\n)$//. Don't use capturing where it's not needed.

In fact - grouping is wasteful for single character alternation. Use a character class instead $user =~ s/[\r\n]$//.

And even better use chomp() chomp($user).

use constant PER_LINE => 20;

my @out;
do {
    @out = ();
    while(<FILE>) {
        push @out, $_;
        last if not 1 .. PER_LINE;
    }
    chomp @out;

    print PIPE join ",", @out;
    print PIPE "\n" if @out;
} until @out != PER_LINE;
[download]

See Mark-Jason Dominus' excellent Program Repair Shop and Red Flags article series on Perl.com for many introductory pointers on writing good code.

Update: D'oh! Fixed a tiny but nasty thinko in the code.

Makeshifts last the longest.

open (FH, $file) or die "$file: $!";
# need to do it once to initialize $.
push @content, scalar (<FH>);
while ($. < LINE_COUNT) {
    push @content, scalar (<FH>);
}
close (FH);
[download]

Hi monks!

First of all, do not use \n\r to cope with/match foreign systems' newlines! chomp appears to be better but it's not (that is, it works only for files in a somewhat compatible format).

Please, please read this node for an expanation of this.

Another trick when iterating over something of arbitrary size, while spitting something out (or doing whatever) at each chunk of data of a given size, use the modulo function (%). This function repeatedly goes zero whenever the chunk size is hit, and is nonzero in between. Here's my try on this:

# tested, but might not exactly match what anonymous
# was doing (added newline output after each chunk, 
# blank after comma seperator,...)

use constant CHUNK_SIZE => 20;

open(FILE, $filename) 
  or die "Can't open $filename: $!\n";

  while(<FILE>)
  {
    s/\012(?:\015)?|\015(?:\012)?//g;
    push @users, $_;

      unless($. % CHUNK_SIZE)
      {
        print join(', ', @users), "\n";
        @users = ();
      }
  }

print join(', ', @users); # Output what's left.
close FILE;
[download]

Of course one could also say unless(@users == CHUNK_SIZE) in this case (since scalar @users actually works as a subcounter here). But, oh well, I just wanted to demonstrate a neat trick. But when you want to interrupt a loop every few passes, using only a total counter modulo really comes in handy. ;) When you think "do x on every n^th line/iteration/pass", think modulo.

So long,
Flexx

Updated: Added last paragraph after first submitting. Made braces in s/// noncapturing (++diotalevi).