defining a new var on the spot

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

greeting holy ones !

Can I define a new variable with a name that stored in another variable?
for example:

# if I have:
$name = 'newVar';

I would like somehow to have a new variable $newVar
[download]

Actually, on runtime I have a regexp, something like:

$tmp =~ /(.+)(\d+)$/;
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and I want to store something in an array by the name stored in $1 (from the regexp) under the index $2 (from the regexp too), the thing is that if the array doesn't already exist, I want to create it on the spot (and initialize it's $2 index). B.T.W. I don't have the names of the arrays in advance, otherwise I would have predefined them.

Hotshot

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Re: defining a new var on the spot by davorg (Chancellor) on Dec 11, 2001 at 18:33 UTC
Yes you can do it. Look up "symbolic references" in any decent Perl book and you'll see an explaination of how to do it - right next to an explaination of why it's such a bad idea. For a good explaination of why you shouldn't do it see these three articles. It's such a bad idea that if you run your programs under `use strict` (as everyone should do) then symbolic references are explicity flagged as an error. A much better idea would be to create a hash or arrays (perhaps call it `%arrays` where you can store these values. `my %arrays; $tmp =~ /(.+)(\d+)$/; $arrays{$1}->[$2] = 'some value';` [download] Oh, and this is a very frequently asked question round here. I find it impossible to believe that Super Search wouldn't have shown you many nodes all saying the same thing. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply] [d/l]
Re: defining a new var on the spot by merlyn (Sage) on Dec 11, 2001 at 21:51 UTC
Can I define a new variable with a name that stored in another variable? I always read this as "Can I poke myself in the eye with a sharp stick?". Yes, you can. If the answer is "define a new variable with a name defined by another variable", you've asked the wrong question. Back up a step. What's the problem you're really solving? -- Randal L. Schwartz, Perl hacker	[reply]
Re: defining a new var on the spot by MZSanford (Curate) on Dec 11, 2001 at 18:30 UTC
You need SymRefs. Somthing like : `$tmp =~ m/(.+)(\d+)$/; ${$1} = $2;` [download] But, There are great many nodes in Super Search which i suggest reading, as this is usually a poor coding practice. If you read the nodes, and feel this is still needed, then the above would be the way to do it. `$ perl -e 'do() \|\| ! do() ;' Undefined subroutine &main::try` [download]	[reply] [d/l] [select]
Re: defining a new var on the spot by mirod (Canon) on Dec 11, 2001 at 18:43 UTC
This question has been asked so many times... ;-( You don't want to do this. It is dangerous. See Dominus's expalnations on Why it's stupid to 'use a variable as a variable name'. If you don't know the name of the array, then use a hash: `#!/bin/perl -w use strict; my %tmp; while( my $tmp=<DATA>) { if( $tmp=~ /^(.+)(\d+)$/) { $tmp{$1}->[$2]= 'foo'; # don't you love auto-vivification? } } __DATA__ foo2 foo5 foo0 bar bar2 bar1 foo3` [download]	[reply] [d/l]
Re: defining a new var on the spot by andye (Curate) on Dec 11, 2001 at 18:42 UTC
Hotshot, others have explained why using symbolic references is a bad idea, here's an alternative: `my %hash_of_arrays; $tmp =~ /(.+)(\d+)$/; $hash_of_arrays{$1}->[$2] = $the_thing_to_store ; use Data::Dumper; print Dumper(\%hash_of_arrays);` [download] hth, andy. Update: dammit, davorg's already said that! I plead snow blindness.	[reply] [d/l]
Re: defining a new var on the spot by strat (Canon) on Dec 11, 2001 at 18:33 UTC
You could try to do this with eval: `$name = 'anyVarName'; eval ("\$$name = 20;"); print $anyVarName;` [download] Best regards, `perl -e "print a\|r,p\|d=>b\|p=>chr 3**2 .7=>t and t"`	[reply] [d/l] [select]