Use of uninitialized value in open

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

My code is :

#!/usr/bin/perl -w
use strict;
my $LOGFILE;
my $line;
$LOGFILE = "access.log";
open(LOGFILE) or die("Could not open log file.");
foreach $line (<LOGFILE>) {
    
    # do line-by-line processing.
}
close(LOGFILE);


I get a very surprising :

$ perl prov.pl
Use of uninitialized value in open at prov.pl line 7.
Could not open log file. at prov.pl line 7.
[download]

I do not understand this error and I ask for the wisdom of the great Mongs. Thank you in advance. Pierre Couderc

Comment on Use of uninitialized value in open Download Code

Replies are listed 'Best First'.
Re: Use of uninitialized value in open by Corion (Patriarch) on Jun 10, 2008 at 08:16 UTC
Usually, Perl is right with its error message. You're not giving the filename to open and hence Perl complains that it doesn't know what to do: `open(LOGFILE)` [download] You need to give `open` the filename to open, and I recommend using lexical filehandles if your version of Perl supports them (since 5.6.0): `open my $fh, "<", $LOGFILE or die "Couldn't open '$LOGFILE': $!";` [download]	[reply] [d/l] [select]
Re: Use of uninitialized value in open by moritz (Cardinal) on Jun 10, 2008 at 08:34 UTC
Corion already gave the correct answer. Let me add pointers to the documentation. "perldoc -f open" documents the open function. If you want a gentler introduction, "perldoc perlopentut" provides a nice tutorial about how to use open in its various forms. You can do much more than just opening files it ;-)	[reply]
Re^2: Use of uninitialized value in open by pcouderc (Monk) on Jun 10, 2008 at 08:38 UTC
Thank you two. My mistake is too that I took this snippet form the web, where it is wrong, and I did not think to suspect it...	[reply]
Re^3: Use of uninitialized value in open by ikegami (Patriarch) on Jun 10, 2008 at 10:19 UTC
I suspect the web version didn't have "`my $LOGFILE;`". It's using an old syntax you'd best avoid in favour of the one Corion showed.	[reply] [d/l]
Re: Use of uninitialized value in open by cdarke (Prior) on Jun 10, 2008 at 09:05 UTC
One other thing if I may, when reporting an error from open is is usually best to include the filename and the reason for the failure ($!), for example: `open(my $hlogfile,'<',$LOGFILE) or die "Could not open $LOGFILE: $!";` [download]	[reply] [d/l]
Re: Use of uninitialized value in open by linuxer (Curate) on Jun 10, 2008 at 09:45 UTC
Just another thing: replace that foreach with while to read from a filehandle. `#!/usr/bin/perl use strict; use warnings; my $logfile = 'access.log'; open my $logh, '<', $logfile or die "$logfile: open failed: $!"; while ( my $line = <$logh> ) { # do line-by-line processing } close $logh or die "$logfile: close failed: $!"; # or die ... not really necessary here, but my fingers type that autom +atically nowadays...` [download]	[reply] [d/l]