Uninitialized Value

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

Good Afternoon Monks,
My question is not so much a question but an explanation is needed concerning the following code:

#!/usr/bin/perl -w

use strict;
use warnings;

my $file = "data.txt";       

local $^I = ".bak";
local @ARGV = ($file);
while (<>) {
chomp;
my @field = split(':');
if ($field[1] =~ s/E/L/g) {
print "$field[0]:$field[1]\n";
} elsif ($field[1] =~ s/L/E/g) {
print "$field[0]:$field[1]\n";
} else {
print "$_\n";
}
}
unlink("$file.bak");

print "UPDATED!!";

sleep 5;
exit();

__DATA__
1:E
2:L
3:L
[download]

As you can see once the code is executed it does change the L to an E and vice versa. My question is why is it saying use of uninitialized value in $field1 in substitution ring when in fact $field1 does have a value? Thanks for the clarification.

Comment on Uninitialized Value Download Code

Replies are listed 'Best First'.
Re: Uninitialized Value by choroba (Cardinal) on May 18, 2015 at 16:32 UTC
I'm not getting the warning with the data you provided. Maybe there's an empty line at the end of the input file? Please, indent the code. لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply]
Re^2: Uninitialized Value by PilotinControl (Pilgrim) on May 18, 2015 at 16:47 UTC
That must have been it. I deleted the data.txt file and made a new one and that error did not show up. Now how do I avoid that from happening? Is there a way for the code to ignore the whitespace or any type of null in the data file?	[reply]
Re^3: Uninitialized Value by pme (Monsignor) on May 18, 2015 at 16:53 UTC
Just add after 'chomp;': `next unless length;` [download]	[reply] [d/l]
Re^4: Uninitialized Value by Athanasius (Archbishop) on May 18, 2015 at 17:27 UTC
Re^5: Uninitialized Value by PilotinControl (Pilgrim) on May 18, 2015 at 18:14 UTC
Re^3: Uninitialized Value by vinoth.ree (Monsignor) on May 18, 2015 at 17:30 UTC
Is there a way for the code to ignore the whitespace or any type of null in the data file? `while (<FILE>) { if ($_ =~ /^$/) { print "it's blank\n"; next; #process next line } else { print "it's NOT blank\n"; } }` [download] `if($_ =~ /^$/)` can also be written as if(/^$/) *All is well. I learn by answering your questions...*	[reply] [d/l] [select]
Re^4: Uninitialized Value by marinersk (Priest) on May 18, 2015 at 19:13 UTC
Re^4: Uninitialized Value by Not_a_Number (Prior) on May 18, 2015 at 20:07 UTC
Re: Uninitialized Value by Not_a_Number (Prior) on May 18, 2015 at 17:25 UTC
Anything wrong with the following? `tr/EL/LE/, print while <DATA>; __DATA__ 1:E 2:L 3:L` [download]	[reply] [d/l]
Re: Uninitialized Value by GotToBTru (Prior) on May 18, 2015 at 16:50 UTC
I don't see that `$field[1]` has a value. It depends entirely on the input. For a simple solution, just add a print command prior to the split so you can see what the contents are; they are probably not what you think they are. Also, I would suggest getting familiar with the debugger. Dum Spiro Spero	[reply] [d/l]
Re^2: Uninitialized Value by PilotinControl (Pilgrim) on May 18, 2015 at 18:12 UTC
Field 1 does have a value...it is either L or E	[reply]
Re^3: Uninitialized Value by GotToBTru (Prior) on May 18, 2015 at 18:19 UTC
I see that you have later figured out what the problem was. If you used your DATA as input, you don't get that error. That would have been a hint to compare it to your actual input file. Dum Spiro Spero	[reply]