Variable scope headaches

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

Hey guys,

I am attempting to assign values to variables like this:

foreach (@tagvalue) {
    if ($_ =~ /([\w,_]+):([0-9]+)/) {
      ${$1} = $2;
    } else { die "Failed to assign value to $1\n"; }
  }
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The result is that within the foreach loop all is good, but outside of it the variables are empty... I tried to use

our ${$1} = $2;
[download]

but get an error on execution: 'Can't declare scalar dereference in "our"'.

./headbang

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Re: Variable scope headaches by jdporter (Paladin) on Jul 26, 2012 at 16:29 UTC
Trying to use a variable as a variable name (i.e. "symbolic references") is generally considered a bad idea. There is an item in the perlfaq about this: How can I use a variable as a variable name?. I highly suggest you read this. It is considered critical enough that it is explicitly detected and forbidden by use strict; - the inclusion of which is universally considered good practice. Instead, use a hash variable: `my %tag_value; foreach ( @tagvalue ) { if ( /([\w,_]+):([0-9]+)/ ) { $tag_value{$1} = $2; } else { die "Failed to assign value to $1\n"; } }` [download] By the way I think your die statement is going to have a problem, in that `$1` will not be set (at least not to what you think) if it ever gets executed. If the pattern match (regex) fails to match, then none of the positional variables (`$1`, etc.) get set. Instead, you might say something like: `die "Failed to match tag/value in '$_'\n";` [download] I reckon we are the only monastery ever to have a dungeon stuffed with 16,000 zombies.	[reply] [d/l] [select]
Re^2: Variable scope headaches by nikmit (Sexton) on Jul 27, 2012 at 07:49 UTC
Thanks jdporter I actually had read that perlfaq item, obviously it didn't quite sink in :) Works now, and code looks better. Thanks for pointing out the 'die' statement error too. I have removed that block of code now but clearly its one to watch out for. nik	[reply]