perl, build strings from several variables content

Question

Here is my starting point:

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

my %hash_a = ( 
"num" => 7, 
"date" => 20221104, 
"prath" => "1.1.10", 
"antema" => "1.1.15" );


my %hash_b = ( 
"num" => 8, 
"date" => 20221105, 
"prath" => "1.1.16", 
"antema" => "1.1.19" );

my %hash_c = ( 
"num" => 9, 
"date" => 20221112, 
"prath" => "1.1.20", 
"antema" => "1.1.39" );

from this I want to make these strings using a loop, if possible without using any trick like building variable names through a loop to get 'hash_a', 'hash_b', 'hash_c'. I was used to use multidimensional arrays for such things in python.

07_class_date_20221104_-_starting_verse_1.1.10_-_closing_verse_1.1.15.mp4

08_class_date_20221105_-_starting_verse_1.1.16_-_closing_verse_1.1.19.mp4

08_class_date_20221112_-_starting_verse_1.1.20_-_closing_verse_1.1.39.mp4

What does "without using any trick like building variable names through a loop to get ...." mean? Are you referring to the names of the hash variables, %hash_a etc? Perhaps you should put all those hashes in another variable, like an array. my @all = ( { num => 7, .... }, { num => 8, .... }, ....); and then loop over the array — TLP
– TLP, Commented Nov 22, 2022 at 15:47
Also, you should specify what your question is about. Is it about making the strings, or about looping over the variables? — TLP
– TLP, Commented Nov 22, 2022 at 15:49

TLP · Accepted Answer · 2022-11-22 15:56:51Z

2

I take it your question is more about looping over the variables, and not so much about building the string.

Usually you would not make a bunch of one record hashes and then try to loop over them, like you are doing with %hash_a, %hash_b etc. I would put them all in a single structure, in this case an array:

my @all = (
{ 
    "num" => 7, 
    "date" => 20221104, 
    "prath" => "1.1.10", 
    "antema" => "1.1.15" 
},
{
    "num" => 8, 
    "date" => 20221105, 
    "prath" => "1.1.16", 
    "antema" => "1.1.19" 
},
{
    "num" => 9, 
    "date" => 20221112, 
    "prath" => "1.1.20", 
    "antema" => "1.1.39" 
});

Then you can simply loop over the array:

for my $record (@all) {
   my $num = $record->{num}; # etc...

And build your string with sprintf

answered Nov 22, 2022 at 15:56

TLP

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2 Comments

user1850133 Over a year ago

It's actually an array of hashes. I did not know this was possible in perl. What about @all = { "num" => { 7, 8, 9}, "date" => {...}, ...}?

TLP Over a year ago

@user1850133 Hashes are not ordered, so it will not retain the original order of the values. If you want order, you use an array, i.e.: @all = ( num => [ 7, 8, 9 ], date => [ ....] .... The angle brackets [ ... ] create anonymous array references. If you have a preferred identifier to look up records, you can make that the main key in the hash: %all = ( 7 => { date => "22222", prath => "1.1.1", ... }, 8 => { .... } );. Then you can loop over key names for my $key (keys %hash)

Håkon Hægland · Accepted Answer · 2022-11-22 15:37:00Z

0

Here is an example:

use feature qw(say);
use strict;
use warnings;
use experimental qw(declared_refs refaliasing);

my %hash_a = (
    "num"    => 7,
    "date"   => 20221104,
    "prath"  => "1.1.10",
    "antema" => "1.1.15"
);


my %hash_b = (
    "num"    => 8,
    "date"   => 20221105,
    "prath"  => "1.1.16",
    "antema" => "1.1.19"
);

my %hash_c = (
    "num" => 9,
    "date" => 20221112,
    "prath" => "1.1.20",
    "antema" => "1.1.39"
);

sub get_str {
    my \%hash = $_[0];

    sprintf "%02d_class_date_%s_-_starting_verse_%s_-closing_verse_%s.mp4",
      $hash{num}, $hash{date}, $hash{prath}, $hash{antema};
}

for my $ref (\%hash_a, \%hash_b, \%hash_c) {
    my $str = get_str($ref);
    say $str;
}

Output:

07_class_date_20221104_-_starting_verse_1.1.10_-closing_verse_1.1.15.mp4
08_class_date_20221105_-_starting_verse_1.1.16_-closing_verse_1.1.19.mp4
09_class_date_20221112_-_starting_verse_1.1.20_-closing_verse_1.1.39.mp4

edited Nov 22, 2022 at 15:37

answered Nov 22, 2022 at 15:28

Håkon Hægland

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4 Comments

user1850133 Over a year ago

well, what if i have a lot of hashes such as hash_a, hash_b... having everything in only one variable (or array, or hash) is what seems the right way.

Håkon Hægland Over a year ago

@user1850133 Yes then you put them in an array. you can define an array of hashes like this my @array = (\%hash_a, \%hash_b, ...)

user1850133 Over a year ago

With "a lot" I was meaning, so many that it might be tedious to write the list of variables.

Håkon Hægland Over a year ago

@user1850133 You can also define the array like this my @array = ({a => 1, ...}, {b=>2, ...}, ...) This is an array of hashes also

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