Using Variable Value as Variable Name

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

I've searched high and low, and I still cannot get this to work. Any suggestions are welcome! TIA

#!/usr/local/bin/perl

use strict;
use warnings;
no strict "subs";
no strict "refs";


my $line = 'fields:  name addr zip state city';
my $var_city;
print "$line\n";
$line =~ s/[-)(]//g;
my @columnNames = split(/\s+/, substr($line,9));
print @columnNames;
print "\n\n";
my $acount = 0;
foreach my $name (@columnNames) {
        $acount++;
        print "name is: $name\n";
        ${var_."$name"} = $acount; 
        #print "nname is: ${"$name"}\n"
}
print "this should display 5: $var_city\n";
[download]

Here is the output:

fields:  name addr zip state city
nameaddrzipstatecity

name is: name
name is: addr
name is: zip
name is: state
name is: city
Use of uninitialized value $var_city in concatenation (.) or string at
+ G:\Projects\WebLogReporting\VarValAsVarName.pl line 28.
this should display 5:
[download]

Comment on Using Variable Value as Variable Name Select or Download Code

Replies are listed 'Best First'.
Re: Using Variable Value as Variable Name by toolic (Bishop) on Jun 28, 2012 at 13:38 UTC
This is a FAQ: How can I use a variable as a variable name? `perldoc -q variable` [download]	[reply] [d/l]
Re^2: Using Variable Value as Variable Name by kennethk (Abbot) on Jun 28, 2012 at 13:58 UTC
See also Why it's stupid to use a variable as a variable name and, if still motivated, Symbolic references. The relevant line is Lexical variables (declared with my()) aren't in a symbol table, and thus are invisible to this mechanism. #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.	[reply]
Re: Using Variable Value as Variable Name by locked_user sundialsvc4 (Abbot) on Jun 28, 2012 at 14:02 UTC
Let me strongly echo what I am sure is a pretty-universal sentiment here: don’t expose the variable-name space, even if you find that you can. This creates a program that is not only un-debuggable, but also wantonly open to sabotage. (And, yeah, you have to think about things like “sabotage.”) If you want to open access to specific variables’ values by name, here is one safe way to do so: create a hash, whose keys are the variable-names, and whose contents for each key is a reference to that variable. This is a controllable and debuggable situation, because “not just any ol’ name you might come up with” can be used; only what `exists()`. Now, presto!, comes the first obvious simplification: why use a variable-name when you can simply refer to the hash? Even though we like to say “TMTOWTDI™ == There’s More Than One Way To Do It,” there are definitely ways that are recommend vs. others that are not...
Re: Using Variable Value as Variable Name by Anonymous Monk on Jun 28, 2012 at 14:03 UTC
Plus, there's always the series of three posts by Mark-Jason Dominus on Why it's stupid to `use a variable as a variable name'	[reply]
Re^2: Using Variable Value as Variable Name by umama (Initiate) on Jun 28, 2012 at 14:21 UTC
Thanks to all for the info. I'm an new to Perl, and was able to do this in PHP. I'm new to PHP as well. I'm an old Cobol/SAS programmer, and I think I have a long way to go. :-)	[reply]
Re^2: Using Variable Value as Variable Name by umama (Initiate) on Jun 28, 2012 at 14:25 UTC
Additional info... my reason for doing this is that I'm processing text files for loading to a database and the column order can vary by file.	[reply]
Re^3: Using Variable Value as Variable Name by kennethk (Abbot) on Jun 28, 2012 at 14:41 UTC
A hash is a much more natural way of dealing with this, and IMHO one of Perl's greatest strengths (the other being regular expressions). You could even use `lock_keys` from Hash::Util to protect yourself from typos. #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.	[reply] [d/l]
Re^2: Using Variable Value as Variable Name by Anonymous Monk on Jun 28, 2012 at 14:04 UTC
Boy, either I am a slow typer, or the responses come really quick here. Didn't mean to post a duplicate link.	[reply]
Re: Using Variable Value as Variable Name by Anonymous Monk on Jun 28, 2012 at 13:30 UTC
You really ought to search before you post. This has been asked MANY times. The answer is: Why would you want to do that?!? Most likely you want a hash, sometimes its a reference to a variable, sometimes it is a more complex data structure.	[reply]
Re^2: Using Variable Value as Variable Name by umama (Initiate) on Jun 28, 2012 at 13:35 UTC
I have searched. Thanks so much for your friendly help.	[reply]