Use of uninitialized value in concatenation (.) or string at perl.pl line 216, <$file> line 18.

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

Hi, why am I getting the following warning when the below piece of code is getting executed?

my $file;
my @files;
    open $file, '<',"$options{c}" or die "could not open '$file' $!\n"
+;
    @files = <$file>;
[download]

Comment on Use of uninitialized value in concatenation (.) or string at perl.pl line 216, <$file> line 18. Download Code

Replies are listed 'Best First'.
Re: Use of uninitialized value in concatenation (.) or string at perl.pl line 216, <$file> line 18. by chrestomanci (Priest) on Dec 15, 2010 at 10:33 UTC
From your code, it looks like `$options{c}` contains the filename you want to read from, and `$file` is your file handle. If the open fails for any reason, then the filehandle stored in `$file` will be undefined, but you are attempting to include it in the `die` error message. In your die error message, you have said 'open', I suggest you change that to 'read from' so that the end user knows what the script it trying to do. Also, there is a feature of the `die` command, where if the die string is terminated with a newline, it is output literally, but if you omit the new line, you get the line number as well, which is helpful for debugging. Line 3 of your code should probably read: `open $file, '<', $options{c} or die "could not read from '$options{c}' + $!";` [download]	[reply] [d/l] [select]
Re: Use of uninitialized value in concatenation (.) or string at perl.pl line 216, <$file> line 18. by ELISHEVA (Prior) on Dec 15, 2010 at 10:26 UTC
Unless Perl is lying to you one of the following three variables is undefined `$file`, the value assigned to 'c' in your `%options` hash (i.e. `$options{c}`), or `$!`. If this is indeed your code, I'd lay bets on `$file` as you declared it but never gave it a value.	[reply] [d/l] [select]
Re: Use of uninitialized value in concatenation (.) or string at perl.pl line 216, <$file> line 18. by fisher (Priest) on Dec 15, 2010 at 10:31 UTC
try this: `my $file; my @files; open $file, '<', "$options{c}" or die "could not open \"$options{c +}\": $!"; @files = <$file>;` [download] self-explanatory code, isn't it?	[reply] [d/l]
Re: Use of uninitialized value in concatenation (.) or string at perl.pl line 216, <$file> line 18. by Anonymous Monk on Dec 15, 2010 at 11:06 UTC
If you use autodie you won't have to add `or die` or get confused about which variable contains the filename (which, FWIW, we discussed this on december 3rd) :) `use autodie; open my $file , '<', $options{c}; my @files = <$file>; close $file;` [download]	[reply] [d/l] [select]