How do i concatenate a string to an array variable inside the loop and access array elements?

Question

I have three arrays. I want to access elements of these three arrays by changing the array names inside a for loop.

I tried concatenating a string to the array variables inside the for loop but its not printing the array elements.

   #!/usr/bin/perl
   my $iterator;
   @data_1 = (10,20,30,40,50);
   @data_2 = ('a','b','c','d','e');
   @data_3 = (-10,-20,-30,-40,-50);

   for ($field = 1; $field < 4; $field++)
   {
    $iterator = "\$data_$field";
    print "iterator = $iterator\n";
    print "$iterator[0]";
   }

Actual output -

   iterator = $data_1
   iterator = $data_2
   iterator = $data_3

Expected output -

   iterator = $data_1
   10
   iterator = $data_2
   a
   iterator = $data_3
   -10

Please guide. Thanks.

ALWAYS use use strict; use warnings;

ikegami
– ikegami

2019-08-17 19:24:32 +00:00
Commented Aug 17, 2019 at 19:24 — ikegami
– ikegami, Commented Aug 17, 2019 at 19:24

tinita · Accepted Answer · 2019-08-17 18:03:03Z

3

Using variable names with other variables is usually a bad idea.

This is why arrays and hashes have been invented. In your case you only need another array:

use warnings;
use strict;
use 5.010;

my @data_1 = (10,20,30,40,50);
my @data_2 = ("a" .. "e");
my @data_3 = (-10,-20,-30,-40,-50);
# put arrays into another array which you can access by index
my @data = \(@data_1, @data_2, @data_3);

for my $field (0 .. 2) {
    my $row = $data[ $field ]; 
    say $row->[0]; 
}

Does this work for you?

answered Aug 17, 2019 at 18:03

tinita

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Comments

Kirk · Accepted Answer · 2019-08-18 18:20:49Z

0

Thanks to the pointer by tinita, I edited what I originally posted to closely match what you asked for as the output.

#!/usr/bin/perl

use warnings;
use strict;
use 5.16.3; 
# depending on what version your server is using, you would need to 
# declare this in order to use "say". On my server it would not allow
# the use of "say" unless I specifically declare which version it was 
# using.

my $output="Testing Iteration Output<br>Perl Version: " . $^V . "<br><br>"; 
# the $^V will help you find your version.

my @data_0 = (10,20,30,40,50);
my @data_1 = ("a" .. "e");
my @data_2 = (-10,-20,-30,-40,-50);

# put arrays into another array which you can access by index
# Note, I renamed the arrays to begin with 0, just for the reference in the output.
my @data = \(@data_0, @data_1, @data_2);

for my $field (0 .. 2) {
    my $row = $data[ $field ]; 
    $output.="iterator = \$data_" . $field . "<br>" . $row->[0] . "<br>"; 
}

print "Content-Type: text/html; charset=ISO-8859-1 \n\n";
print qq|$output|;
exit;

Then, this is what came as the output

Testing Iteration Output
Perl Version: v5.16.3

iterator = $data_0
10
iterator = $data_1
a
iterator = $data_2
-10

edited Aug 18, 2019 at 18:20

answered Aug 17, 2019 at 16:23

Kirk

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2 Comments

tinita Over a year ago

This is only working with package variables and not variables declared with my, and it doesn't work with use strict. So I wouldn't recommend this

Kirk Over a year ago

Thank you for pointing that out. I appreciate it. I modified my answer to include your pointer, and to add the syntax the user was asking for. I hope that is ok with you. The way I wanted to show the output is to gather it as it's working, then print it at the end. I guess because I am always thinking about how the data might be used several times in the eventual output.

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