What does "Useless use of string in void context" mean?

[Tama]

I run a tiny little Perl script on my site that I bodged up by myself. The script runs fine, but I get the following line in my servers error logs

Useless use of string in void context at linklog.cgi line 10.

The script looks like this:

#!/usr/bin/perl -w

#use strict;

#Thanks to Nuxy from [URL unfurl="true"]http://www.tek-tips.com[/URL] for the base of this script

my $logfile = "/home/vorb/[URL unfurl="true"]www/link/linklog.csv";[/URL]
my $time = gmtime;

open (FILE, ">>$logfile") || "can't open $logfile";
print FILE ("$ENV{'QUERY_STRING'},$ENV{'HTTP_REFERER'},$time\n");
close (FILE);
exit;

I know I'm missing something obvious, but I can't work out what - any ideas?

Cheers
Tama

 

[zephan]

So obvious that you can expect nobody can see it :

open (FILE, ">>$logfile&quot || or die("can't open $logfile"

instead of

open (FILE, ">>$logfile&quot || "can't open $logfile";

 

[sleipnir214]

The line should read:

open (FILE, ">>$logfile&quot or die "can't open $logfile";

You weren't explicitly telling perl what to do with the string literal.

In situations where you have a line that will perform an action, or if that one fails a default action, use the "or" operator, not the "||" operator. "or" has a lower precedence than "||", which reduces the chances that you will ge weird behavior from your code in the event that the first action uses logical operators.

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[zephan]

Sorry Tama, there's a mistake in my corrected line.
Thanks sleipnir214.

 

[Tama]

Hi guys, thank you for your quick responses.
I've changed the line to
open (FILE, ">>$logfile&quot or die "can't open $logfile";


And it's now spitting out this line

Premature end of script headers: /www/vorb/cgi-bin/linklog.cgi

in the error logs.

 

[missbarbell]

When 'die' is called it terminates the program and spits out the message you give it. If this is running from a CGI script the message gets sent to the server error log, and the default classic '500 Internal Server Error' gets sent to the browser.

The problem lies with your $logfile. For some reason (possible the file permissions don't allow it to be appended to) the script is failing. There are 2 things you could do to see the error.

First change the line to:

open (FILE, ">>$logfile&quot or die "can't open $logfile: $!\n";

The $! internal variable should give a more verbose description of the problem.

Or secondly, you could add the following to the top of your code after the shebang line (#!/usr/bin/perl):

use CGI::Carp qw(fatalsToBrowser);

This will then send nice error messages to your browser. However, make sure the line is removed for production code, as it can sometimes give away a bit too much information. Barbie
Leader of Birmingham Perl Mongers

http://birmingham.pm.org

 

[Tama]

Hi msbarbell

Sorted! Thank you for all your help guys... 15 hours in front of the PC today... yargh...

Cheers
Tama