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

I am using a couple of subroutines in a basic script to parse a text file:

#!/usr/bin/perl -w
use strict;
my $text, $ques, $ans;

open(IN, "<$ARGV[0]")||die"Couldn't open $ARGV[0]: $!\n";
while(<IN>){
  $text = &do_one_thing($_);
  ($ques, $ans) = &do_another_thing($text);
  print $ques." :: ".$ans."\n";
}
close(IN);

sub $do_one_thing{
  my $line=uc($_);
  $line =~ s/this/that/g;
  return($line);
}

sub $do_another_thing{
  my $another_line, $one, $two;
  $another_line = $_;
  ($one, $two) = $another_line =~ /(.[^\*]*)\*(.*)/;
  return($one, $two);
}

[download]


So my question is, why do $ques and $ans remain lowercase; more generally, why does the second subroutine again use $_ from the main body of the program, rather than the local $_ (which I'm guessing ought to be $text)? I can rearrange the script pretty simply to make it work (by not using the extra variable) which I did, but it made me curious as to why it doesn't work the way I've written it above...

thanks!

Replies are listed 'Best First'.
Re: Why is this incorrect?
by rafl (Friar) on Mar 17, 2006 at 02:18 UTC

    $_ is a global.

    Beside that to get the first parameter you passed to your subs you should use

    my $line = lc $_[0];
# and 
$another_line = $_[0];

    [download]

    as it is the first element in the @_ array, which contains all arguments to the sub.

    Beside that you should not use $ in sub names, you should not use & in function calls and you should use warnings.

    Cheers, Flo

[reply]
[d/l]
      you can override the $_ for the subrouting by declaring it with 'local'. This may make things easier in the future for you.
[reply]
      I guess I should look this up, but why should '&' not be used in function calls? thanks for the other advice!
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Re: Why is this incorrect?
by japhy (Canon) on Mar 17, 2006 at 02:19 UTC
    You've failed to show working code. And your parameter passing to your functions is wrong. You need to get the arguments from the @_ array, not from $_.
    Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
    How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart
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Re: Why is this incorrect?
by spiritway (Vicar) on Mar 17, 2006 at 04:13 UTC

    In looking at your code, the first thing I noticed was your line 3:

    my $text, $ques, $ans;

    Right away you should have gotten an error about globals needing explicit package name. To declare multiple variables you need to enclose them in parenthese:

    my ($text, $ques, $ans);

    The same problem exists on line 20:

    my $another_line, $one, $two;

    Next, you have:

    sub $do_one_thing{...;

    which is also an error. You need to remove the sigils from this and the subsequent sub.

    From what you've shown, I can't imagine this program producing any output.

[reply]
[d/l]
[select]
      you're right, it probably doesn't produce any output. i didn't check it. the actual script that I am using is much longer, and I didn't want copy the whole thing - just to ask about what I didn't understand. (sorry for not checking). anyway, despite that I did get the answer to the question I was asking, so thanks a bunch! i was going to add that i don't really know what I'm doing yet, but i suppose an explicit statement was unnecessary!
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Re: Why is this incorrect?
by trammell (Priest) on Mar 17, 2006 at 02:23 UTC
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[d/l]
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