Modulus by zero?

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

In this script, I get the error "Illegal modulus zero," but I can't see why it says that. Any ideas?

use strict;
use warnings;

if(!@ARGV){
    my $line=1;
    $_=<>;
    handlefix();
    open(INFILE, '<', $_) or die "\nCan't open $_: $!\n";
    $_=<>;
    handlefix();
    open(OUTFILE, '>', $_) or die "\nCan't open $_: $!\n";
    while(<INFILE>){
        print OUTFILE "_$line",":     $_" if $line %% 5==0;
        print OUTFILE "         $_" if $line %% 5!=0;
        $line++;
    }   
    close INFILE && close OUTFILE;
}
if(@ARGV){
    my $line=1;
    $_= shift @ARGV;
    handlefix();
    open(INFILE, '<', $_) or die "\nCan't open $_: $!\n";
    $_= shift @ARGV;
    handlefix();
    open(OUTFILE, '>', $_) or die "\nCan't open $_: $!\n";
    while(<INFILE>){
        print OUTFILE "_$line",":     $_" if $line %% 5==0;
        print OUTFILE "         $_" if $line %% 5!=0;
        $line++;
    } 
    close INFILE && close OUTFILE;
}


sub handlefix {
    chomp($_);
    $_=~s/"//g;
    $_=~s/\//\\/g;
    return $_;
}
[download]

Thanks in advance!

Comment on Modulus by zero? Download Code

Replies are listed 'Best First'.
Re: Modulus by zero? by cLive ;-) (Prior) on Nov 16, 2006 at 23:03 UTC
% not %%	[reply]
Re^2: Modulus by zero? by Andrew_Levenson (Hermit) on Nov 16, 2006 at 23:05 UTC
Wow, that was an easy fix. Thanks!	[reply]
Re: Modulus by zero? by pKai (Priest) on Nov 17, 2006 at 07:41 UTC
Now that is interesting… `>perl -MO=Deparse -e "$a if $b %% 5 == 0" $a if $b % %5 == 0; -e syntax OK` [download] So `%5` is some sort of hash!? From perlvar Perl variable names may also be a sequence of digits or a single punctuation or control character. These names are all reserved for special uses by Perl; for example, the all-digits names are used to hold data captured by backreferences after a regular expression match. So the scalar variant of those digit vars are well-known, but the hash variant is "reserved" and serves no special purpose by now.	[reply] [d/l] [select]
Re^2: Modulus by zero? by shmem (Chancellor) on Nov 17, 2006 at 15:11 UTC
The documentation is somewhat misleading at this point. Only all-digit scalars are read-only backreferences to captures, while all-digit hashes and arrays are not, not even read-only. But yes, they might be reserved :-) `perl -le '@2 = 1..3; @1{qw(a b c)} = @2; print "$_=>$1{$_}" for keys % +1' c=>3 a=>1 b=>2` [download] Use of @1, %2 and so on is a common obfuscation technique. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l]
Re^2: Modulus by zero? by ikegami (Patriarch) on Nov 17, 2006 at 17:22 UTC
Also interesting is how the variable doesn't need to be declared, since it is automatically considered a package variable. `>perl -Mstrict -e "@1 >perl -Mstrict -e "my @1 an't use global @1 in "my" at -e line 1, near "my @1" Execution of -e aborted due to compilation errors.` [download] Update: Ah, other special-like variables are like that too. `>perl -Mstrict -e "%! >perl -Mstrict -e "my %! Can't use global %! in "my" at -e line 1, near "my %!" Execution of -e aborted due to compilation errors.` [download]	[reply] [d/l] [select]
Re^2: Modulus by zero? by orderthruchaos (Scribe) on Nov 17, 2006 at 14:11 UTC
IGNORE THIS I think it may be interpreting it as `$b % undef % 5 == 0;` undef would then be converted to zero before processing.	[reply] [d/l]
Re^3: Modulus by zero? by Fletch (Bishop) on Nov 17, 2006 at 14:22 UTC
The `-p` option to B::Deparse can be helpful when precedence questions arise: `$ perl -MO=Deparse,-p -e '$a if $b %% 5 == 0' ((($b % %5) == 0) and $a); -e syntax OK` [download]	[reply] [d/l]
Re^3: Modulus by zero? by orderthruchaos (Scribe) on Nov 17, 2006 at 14:17 UTC
Oops... nevermind... you're right... From the perl DB: `DB<2> x \%5 + 0 HASH(0x500be0) empty hash` [download]	[reply] [d/l]