Arien0611 has asked for the wisdom of the Perl Monks concerning the following question:

hello monks. i have a problem with a subroutine of mine. i dont know if it something wrong with its syntax, and googling it, wasnt much of a help. so, i have this subroutine: 
sub exractSongTitlesFromCueFile{
    my ($cue_file_to_parse) = @_;
    my @album_info;
    my $w = 0;
    open(CUEFILEFOUND, $cue_file_found) || die "Error 003: Could not o
+pen cue file named: $cue_file_found! $!\n";
    while(<CUEFILEFOUND>){
        if($_ =~ /\s+TITLE "(.*)".*/){
            $album_info[$w] = $1 || die "Error 004: Could assign song 
+title to array! $!\n";
#            print "$1\n";
            $w++ || die "Error 005: Could not increment array pointer 
+$!\n";
        }
    }
    close(CUEFILEFOUND);
    return (@album_info);
}
</code

and running the script, would give me this output:

<code>
Error 005: Could not increment array pointer Inappropriate ioctl for d
+evice

[download]
i dont understand what i m doing wrong. i mean, i just want to increment my variable... thanks for your time though, and sorry if my question is a tad stupid. i just dont understand the problem, and i cant search for it somewhere. so any help would be appreciated.

Replies are listed 'Best First'.
Re: weird begginer's problem...
by choroba (Cardinal) on Sep 06, 2012 at 16:16 UTC
    You start with $w == 0. You post-increment it, which means before changing its value, you perform the || die test. Therefore, 0 || die goes the "or" way and dies. Since there was no system failure immediately before the death, the value of $! is meaningless, as documented in Perl Predefined Variables / $OS_ERROR.
    لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
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Re: weird begginer's problem...
by hbm (Hermit) on Sep 06, 2012 at 16:17 UTC

    Hint: 

    perl -e "$w=0; $w++||die"
Died at -e line 1.

perl -e "$w=0; ++$w||die"
# no error

    [download]
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[d/l]
      hm, i knew it would something stupid. i m stupid. i should go and farm some cows, instead of programming. thank you for the help though guys. i appreciate it.
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        I suspect that the rate of incredibly stupid mistakes doesn't actually decrease as you gain experience. We just get less incredulous as we go.

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Re: weird begginer's problem...
by MidLifeXis (Monsignor) on Sep 06, 2012 at 16:23 UTC

    A preference as well, although it may save you some trouble later:

    foo() || die "bar"

    vs

    foo() or die "bar"

    The || is of higher precedence than or. Using or (at least in the action or die pattern) can help avoid some sneaky precedence bugs.

    Update: Added example below

    perl -e 'print 1 - 1 || die "hello"'

    vs

    perl -e 'print 1 - 1 or die "hello"'

    --MidLifeXis

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Re: weird begginer's problem...
by Khen1950fx (Canon) on Sep 06, 2012 at 16:29 UTC
    You'll need to declare $cue_file_found, and you'll also need to use strictures. I ran this and got no errors: 
    #!/usr/bin/perl

use strict;
use autodie;
use warnings;

sub exractSongTitlesFromCueFile {
    my ( $cue_file_to_parse ) = @_;
    my @album_info;
    my $w = 0;
    my $cue_file_found = '/tmp/cue/cue_file';

    open( CUEFILEFOUND, '<', $cue_file_found )
      or die "Could not open cue file named: 
        $cue_file_found! $!\n";
    while (<CUEFILEFOUND>) {
        if ( $_ =~ /\s+TITLE "(.*)".*/ ) {
            $album_info[$w] = $1
              || die "Error 004: 
               Couldn't assign song title to array! $!\n";
            $w++ || die "Error 005: 
               Could not increment array pointer $!\n";
        }
    }
    close(CUEFILEFOUND);
    return (@album_info);
}

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[d/l]

      Does not seem correct, just based on reading, as this version has the same root-cause issue as the first: the $w++ starts out at zero, causing the die to fire the first time through the loop where the TITLE matches.

      --MidLifeXis

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