Why do I keep getting this error message?

dru145 has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

This is driving me crazy. I keep getting the error message Use of uninitialized value in concatenation (.) at /usr/local/apache/cgi-bin/temp line 196 when I run my script with -w. Here is the part of the script where the error is happening:

    188    open (IN,"$header") || die "can't open file $header: $!";
    189    open (OUT,">$output") || die "can't open file $output: $!";
    190     while (<IN>) {
    191      print OUT $_;
    192     } # close while
    193    close(IN) || warn "can't close $header: $!";
    194    close(OUT) || warn "can't close $output: $!";
    195 
    196    my $string = "$month$year1";
    197    my @days = ($day1 .. $day2);
    198    @days = map {$_ .= "$string"} @days;
[download]

Can somebody please tell me what I am doing wrong?

Thanks
<br -Dru

Comment on Why do I keep getting this error message? Select or Download Code

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Re: Why do I keep getting this error message? by dvergin (Monsignor) on Dec 05, 2001 at 22:33 UTC
Either `$month` or `$year1` has not been assigned a value. When an error like this occurs with a variable in a double-quoted string (or its ilk) Perl refers to it as concatenation. It's as if you had typed "My name is " . $myname instead of "My name is $myname" If you want to know which one it is, simply print out each one on lines just before the error line. Or sometimes if I think this may happen again some day. I alter the code (with a reminder of why I left it that way) and just leave it as: `# my $string = "$month$year1"; my $string = $month; # separate vars for easier debug $string .= $year1; # separate vars for easier debug` [download] This way I don't need to come back to remove the print trace statements. And if the problem happens again, I can zero in on it immediately.	[reply] [d/l]
Re: Why do I keep getting this error message? by George_Sherston (Vicar) on Dec 05, 2001 at 23:04 UTC
dvergin is spot on. The only thing I'd add is that if for some reason you want to be able to deal with the occasional appearance of an unititialised value then this wd do the trick (or whatever defaults you favour): `196 my $string = ($month or 'no month') . ($year1 or 'no year');` § George Sherston	[reply] [d/l]
Re: Why do I keep getting this error message? by vek (Prior) on Dec 06, 2001 at 03:20 UTC
Or if you have some reason to suspect that there are valid circumstances where `$month` or `$year1` are not getting assigned, you could always test them: `unless ( $month && $year1 ) { # your error code here... }` [download]	[reply] [d/l] [select]