How to get array of hash arguments using Getopt::Long lib in perl? - perl

Question

I want to take arguments as an array of hashes by using Getopt::Long in my script.
Consider the following command line example:
perl testing.pl --systems id=sys_1 ip_address=127.0.0.1 id=sys_2 ip_address=127.0.0.2
For the sake of simplicity, I'm using two systems and only two sub arguments of each system, i.e., id and ip_address. Ideally, the number of systems is dynamic; it may contain 1, 2 or more and so with the number of arguments of each system.
My script should handle these arguments in such a way that it will store in #systems array and each element will be a hash containing id and ip_address.
Is there any way in Getopt::Long to achieve this without parsing it myself?
Following is pseudocode for what I'm trying to achieve:
testing.pl
use Getopt::Long;
my #systems;
GetOptions('systems=s' => \#systems);
foreach (#systems) {
print $_->{id},' ', $_->{ip_address};
}

Answer 1

Here is an attempt, there might be more elegant solutions:
GetOptions('systems=s{1,}' => \my #temp );
my #systems;
while (#temp) {
my $value1 = shift #temp;
$value1 =~ s/^(\w+)=//; my $key1 = $1;
my $value2 = shift #temp;
$value2 =~ s/^(\w+)=//; my $key2 = $1;
push #systems, { $key1 => $value1, $key2 => $value2 };
}
for (#systems) {
print $_->{id},' ', $_->{ip_address}, "\n";
}
Output:
sys_1 127.0.0.1
sys_2 127.0.0.2

Answer 2

I actually think this is a design problem, more than a problem with GetOpt - the notion of supporting multiple, paired arguments passed as command line arguments I think is something that you'd be far better off avoiding.
There's a reason that GetOpt doesn't really support it - it's not a scalable solution really.
How about instead just reading the values from STDIN?:
#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
my %systems = do { local $/; <DATA> } =~ m/id=(\w+) ip_address=([\d\.]+)/mg;
print Dumper \%systems;
And then you'd be able to invoke your script as:
perl testing.pl <filename_with_args>
Or similar.
And if you really must:
my %systems = "#ARGV" =~ m/id=(\w+) ip_address=([\d\.]+)/g;
Both of the above work for multiple parameters.
However, your comment on another post:
I can't because I'm fetching parameters from database and converting them into command line and then passing it to the script using system command $cmd_lines_args = '--system --id sys_1 --ip_address 127.0.0.0.1'; system("perl testing.pl $cmd_lines_args"); $cmd_lines_args I'll generate dynamically using for loop by reading from database
.. that makes this an XY Problem.
Don't do it like that:
open ( my $script, '|-', "perl testing.pl" );
print {$script} "id=some_id ip_address=10.9.8.7\n";
print {$script} "id=sys2 ip_address=10.9.8.7\n";
etc.

Answer 3

What you are describing,
--systems id=sys_1 ip_address=127.0.0.1 id=sys_2 ip_address=127.0.0.2
appears to be one option that takes a variable number of arguments that are pairs, and come in multiples of two. Getopt::Long's "Options with multiple values" lets you do the following:
GetOptions('systems=s{2,4}' => \#systems);
This lets you specify 2, 3 or 4 arguments, but it does not have syntax for "any even number of arguments" (to cover an arbitrary number of pairs beyond two), and you still have to unpack the id=sys_1 manually then. You can write a user-defined subroutine that handles the processing of --systems' arguments (but does not take into account missing id=...s):
my $system;
my %systems;
GetOptions('systems=s{,}' => sub {
my $option = shift;
my $pair = shift;
my ($key, $value) = split /=/, $pair;
$system = $value if $key eq 'id';
$systems{$system} = $value if $key eq 'ip_address';
});
I would however prefer one of the following schemes:
--system sys_1 127.0.0.1 --system sys_2 127.0.0.1
--system sys_1=127.0.0.1 --system sys_2=127.0.0.1
They're achieved with the following:
GetOptions('system=s{2}', \#systems);
GetOptions('system=s%', \#systems);

Answer 4

I would just parse the --systems arg and quote the "hashes" like this:
perl testing.pl --systems "id=s1 ip_address=127.0.0.1 id=s2 ip_address=127.0.0.2"
Parse like perhaps so:
my($systems,#systems);
GetOptions('systems=s' => \$systems);
for(split/\s+/,$systems){
my($key,$val)=split/=/,$_,2;
push #systems, {} if !#systems or exists$systems[-1]{$key};
$systems[-1]{$key}=$val;
}
print "$_->{id} $_->{ip_address}\n" for #systems;
Prints:
sys_1 127.0.0.1
sys_2 127.0.0.2