Use of uninitialized value $site in concatenation (.) when excute the perl script

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

when I am running the perl script where I user foreach to read the file line by line I got the print message. "Use of uninitialized value $site in concatenation (.) or string at logfile.pl line 13, <LOGFILE> line 19."

#!/usr/bin/perl -w

use strict;
use warnings;
my ($time, $site, $logName, $fullName, $date, $gmt, $req, $file, $prot
+o, $status, $length);
$site;
my $LOGFILE = "config.txt";
open LOGFILE,"$LOGFILE" or die "cannot open file : $!";
foreach my $line (<LOGFILE>) {
    
    ($site, $logName, $fullName, $date, $gmt,
         $req, $file, $proto, $status, $length) = split(' ',$line);
   my $a = "$site\n";
   print "--$a\n";
   my $b = "$logName\n";
   print "==$b\n";
 }
close(LOGFILE);
[download]

Please let me know where I am doing the mistake.

Comment on Use of uninitialized value $site in concatenation (.) when excute the perl script Download Code

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Re: Use of uninitialized value $site in concatenation (.) when excute the perl script by kcott (Archbishop) on Aug 31, 2012 at 09:21 UTC
You probably have blank lines in your input. In the split doco, under "As another special case, ...", you'll see how your pattern (`' '`) is handled specially. Whenever `$line` equals `"\n"`, `split(' ',$line)` will return `()`: all of those 10 variables (`$site, ..., $length`) will be undef (i.e. "uninitialized value"). If you want to ignore them, you can do something like this: `foreach my $line (<LOGFILE>) { next if $line =~ /\A\Z/; ($site, ... ... }` [download] [Aside: `$a` and `$b` are not good choices for variable names as they have special meaning to Perl - see perlvar] -- Ken	[reply] [d/l] [select]
Re^2: Use of uninitialized value $site in concatenation (.) when excute the perl script by Anonymous Monk on Sep 02, 2012 at 14:43 UTC
And, `foreach my $line (<LOGFILE>)` reads the whole LOGFILE straight into memory before starting to enumerate through the lines. (Unless Perl has special-case handling for that case. Which I don't recall Perl having.) The OP should use the iterator form: `while (my $line = <LOGFILE>) {`	[reply] [d/l] [select]
Re: Use of uninitialized value $site in concatenation (.) when excute the perl script by Corion (Patriarch) on Aug 31, 2012 at 08:49 UTC
Have you read the error message? It tells you to look at line 13. It tells you that the variable `$site` in line 13 is undefined. Maybe you should look at where `$site` gets set, and find out why it doesn't seem to have the value you expect.	[reply] [d/l] [select]
Re: Use of uninitialized value $site in concatenation (.) when excute the perl script by nemesdani (Friar) on Aug 31, 2012 at 08:53 UTC
Line 13 is where you set the variable $a (choose another name by the way), and you concatenate the variable $site with a newline. -> There is something wrong with the $site variable, thus with your input(Logfile). Check it. I'm too lazy to be proud of being impatient.	[reply] [d/l]
Re: Use of uninitialized value $site in concatenation (.) when excute the perl script (an aside - code review) by MidLifeXis (Monsignor) on Aug 31, 2012 at 13:07 UTC
Take this or leave it, but there are some practices in your code that have a faint whiff of cargo culting or things that may cause problems later on. I understand that this code may just be an example. Read more... (2 kB) --MidLifeXis	[reply] [d/l]
Re: Use of uninitialized value $site in concatenation (.) when excute the perl script by MidLifeXis (Monsignor) on Aug 31, 2012 at 12:51 UTC
In addition to pointing you at line 13 in your code (as has already been mentioned), the error message also tells you exactly which line in `config.txt` it is having problems with. Read the log file, compare line 13 to a different line that is not reported, and see what the differences are. --MidLifeXis	[reply] [d/l]