You read and modify $_, but it doesn't print.

I've added a print to the program, as per your suggestion. Well, it's still clobbering the output. However, now instead the output files, instead of being completely blank, have the shebang line and the copyright line, then the rest is completly obliterated. None of the text that was previously there, aside from the shebang line, are there.

Right now, the code looks like this:

#!/usr/bin/perl
use strict;
use warnings;

$^I = ".old";

while (<>) {
   if (/^#!/) {
      $_ .= " ## Copyright (C) 2008 me\n";
      print;
   }
}
[download]



I have to say, that a lot of this discussion is completely over my head. To anyone kind enough to repond, please try to bear in mind that I am working on chapter 9 in the Llama book. Thanks!

What happens if you move the print outside of the if construct?

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

Just to make CountZero's good suggestion more obvious, your code should probably look like this:

#!/usr/bin/perl
use strict;
use warnings;

$^I = ".old";

while (<>) {
   if (/^#!/) {
      $_ .= " ## Copyright (C) 2008 me\n";
   }
   print;
}
[download]

The way you had it, the print would only happen on the line where you made the change. This way, every line is printed, whether you changed it or not.

P.S.: I use Windows, hence the double quotes.

This meets the problem statement, no question.

But I have an issue with the problem statement itself. I don't use a real shebang line. Instead, my "shebang" line is this instead:

eval '(exit $?0)' && eval 'exec perl -w -S $0 ${1+"$@"}'
                  && eval 'exec perl -w -S $0 $argv:q'
                  if 0;

# The above invocation finds perl in the path, wherever it may be
[download]

So fortunately the original problem statement doesn't break it, nor does the intended solution do what it's supposed to.

This probably isn't the place to discuss the merits of a real shebang line, but I'll mention one point anyway. My *nix home directory is automounted on countless network machines, and I don't have the time to manage $PATH on every one, etc.

Unless there is a more elegant way than this, I'll do without a shebang.

-QM
--
Quantum Mechanics: The dreams stuff is made of

if (/^#!/) {
would be more accurate as
if ($. == 1 && /^#!/) {

You suggest the use of $., but perlvar cautions with respect to $. that

Because ``<>'' never does an explicit close, line numbers increase across ARGV files (but see examples under eof()).

The OP seems to want to process multiple files from the command line. The relevant example from the entry for eof is:

   # reset line numbering on each input file
    while (<>) {
        next if /^\s*#/;        # skip comments
        print "$.\t$_";
    } continue {
        close ARGV  if eof;     # Not eof()!
    }
[download]

You are being asked to do 'in-place' editing. Re-read the perl command switches, namelly -i. Description also available online in perlrun.

update Thanks ysth. Didn't knew that.

$^I (which the OP uses) is the non-command-line interface to the same functionality.
--
Online Fortune Cookie Search

Cheers
Chris

What in your program is doing the output?