How to convert raw string to variable (variable --> $variable)?

Question

How to convert string to variable (string variable --> $variable)?

Or a list of variables delimited by commas then convert to actual variables.

I have 2 files:

column names file
rows file

I need to match a whole row from the rows file based on a string, and name each row based from the column names file.

Example:

COLUMN NAMES FILE content

name,age,gender

ROWS FILE content

mar,44,m
rich,49,m
glenn,22,m

Now I have a variable string $who = 'glenn'

I will first match it on the ROWS FILE.

Then I need to name its matched contents with an actual variable with its name based on the COLUMN NAMES FILE.

Output:

$name = 'glenn';
$age = 22;
$gender = 'm';

I need something that dynamically changes, creating the needed variables and contents automatically by only updating the content files.

Okay, so if you achieve this, how will you know what variable names to use in the rest of your Perl code? — Borodin
– Borodin, Commented Jul 26, 2016 at 11:08
@Borodin , I am building a universal/standard module at the company where I am working (called using require). Since this will be a module, there will expectations like what are the available variable. And for me not to worry, I will follow the SOLID principle, I can only add but not modify the expected available variables. Thanks for asking. Let me know if I can answer any other questions... — Digimon Digitizer 2
– Digimon Digitizer 2, Commented Jul 26, 2016 at 11:16
It's still a terrible idea to crap all over your namespace like this. What if someone creates a column called /? Or 0? Or ^I? You'll create some HORRIFIC bugs that will be an absolute horror to trace. — Sobrique
– Sobrique, Commented Jul 26, 2016 at 11:24
@Sobrique don't worry, "IT WON'T HAPPEN". Because the column names I am planning to create are based from a ora sql table, which is a production table. — Digimon Digitizer 2
– Digimon Digitizer 2, Commented Jul 26, 2016 at 11:26

Sobrique · Accepted Answer · 2016-07-26 11:18:03Z

9

What you're asking for, is not what you want. This is a bad idea for many many reasons, but they're outlined here: http://perl.plover.com/varvarname.html

What you need for this is a hash, and specifically a slice.

It works a bit like this:

my @header = qw ( A B C );
my @values = qw ( X Y Z );
my %combined;
@combined{@header} = @values; 
print Dumper \%combined;

Gives:

$VAR1 = {
          'C' => 'Z',
          'A' => 'X',
          'B' => 'Y'
        };

(NB: Hashes are explicitly UNORDERED, so you get a random sequence each time you print. That's by design, because they're supposed to be accessed via keys anyway)

So with your data:

#!/usr/bin/env perl
use strict;
use warnings 'all'; 

open ( my $cols, '<', 'cols_file.txt') or die $!;
chomp ( my @cols = split /,/, <$cols> ); #just reads first line. 
close ( $cols );
open ( my $rows, '<', 'rows_file.txt' ) or die $!; 
while ( <$rows> ) {
    chomp;
    my %this_row;
    @this_row{@cols} = split /,/;
    push ( @all_rows, \%this_row );
}
close ( $rows );

print Dumper \@all_rows;

You can then access individual elements from rows e.g.:

foreach my $row ( @all_rows ) {
    print $row -> {name},"\n";
 }

edited Jul 26, 2016 at 11:18

answered Jul 26, 2016 at 11:03

Sobrique

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1 Comment

Digimon Digitizer 2 Over a year ago

Thank you very very very very MUCH! You made my day! It worked like charm! :D I am so glad someone like you answered my question! Thank you so much once again. I have achieved what I need! :)

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