Ok, it is late and my brain is fried. But I cannot see what I am doing wrong. I want call a subroutine, passing two variables as references. My understanding is that this is effectively a "call by name", and any modifications the subroutine makes to the variables within the subroutine scope will be reflected in the main program.

Here is a sample program:

#!/usr/bin/perl -w

$template_file = "test.pl";
$template = "old value";
print "Before call: $template \n";

$cnt = read_template(\$template_file, \$template);

print "$cnt lines read \n";
print "after call: $template \n";


sub read_template {

  my $file_name = ${shift()};
  my $lines_in  = ${shift()};
  my $line_cnt  = 0;

  if (!open (INPUT, "< $file_name")) {
    die "Can't open $file_name as input.";
  } else {
    while (<INPUT>) {
      $line_cnt++;
      $lines_in .= $_;
    }
    close (INPUT);
  }
  return($line_cnt);
}
[download]

and here is the output:

Before call: old value 
29 lines read 
after call: old value
[download]

What wrong assumptions have I made?

By the way, I am calling the subs this way as I am working on a CGI program that I want to make "mod_perl" safe