uninitialized value in substitution

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

Hey monks, I can't figure out what to do to alleviate the error uninitialized value in substitution using the following:

#!/usr/bin/perl -w
#
print "Please put in the username for which you want to setup a virtua
+l host:\n";

my $user = <STDIN>;
my @fields = ();
my $fields = ();

open TPL, "vh_template.tpl";
my @vhost = <TPL>;
close TPL;

foreach my $vhost(@vhost){
        if ($vhost =~ /^ServerName/){
                @fields = split /\./, $vhost;
                $fields = @fields;
                s/$fields\[0\]/$user/; #this line generates the error
                print "$fields[0]\n";
                }
}
[download]

Thanks for your help! John

Comment on uninitialized value in substitution Select or Download Code

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Re: uninitialized value in substitution by ihb (Deacon) on Sep 09, 2004 at 19:40 UTC
You're implicitly binding the `s///` to `$_` which isn't initialized. `s/$fields\[0\]/$user/;` is really `$_ =~ s/$fields\[0\]/$user/;`. `ihb` Read argumentation in its context!	[reply] [d/l] [select]
Re: uninitialized value in substitution by bobf (Monsignor) on Sep 09, 2004 at 19:46 UTC
Your s/// is defaulting to use $_, which is not initialized. If I understand what you're trying to do, use `$vhost =~ s/$fields[0]/$user/`. Note that you shouldn't escape the brackets for the array index. HTH	[reply] [d/l]
Re: uninitialized value in substitution by ikegami (Patriarch) on Sep 09, 2004 at 19:50 UTC
First, you never specify in your code against what you're matching, and you never give a value to $_ (the variable against which matching is done by default). I can't fathom what the line giving the error is trying to do (matching against any of the variables in the snippet woulnd't make sense), so we don't know how to fix this. Second, `my $fields = ();` is the same as `my $fields = undef;`, and in the regular expression, you're refering to this variable instead of the first element of @fields as you probably intended. If you want to match what's in the first element of @fields, try: `s/$fields[0]/$user/`. Of course, that should probably really be: `s/\Q$fields[0]\E/$user/` since @fields holds simple strings, not regexps.	[reply] [d/l] [select]
Re: uninitialized value in substitution by mayhem (Hermit) on Sep 09, 2004 at 19:36 UTC
You should chomp($user) in there somewhere and the line your getting an error on... why don't you just do `$fields[0] = $user;` [download] That should work if i understand what you are trying to do..	[reply] [d/l]