G'day m_jaser,

Here's a very basic example of how you might go about this.

#!/usr/bin/env perl

use strict;
use warnings;

use Data::Dump;
use Getopt::Long qw{GetOptionsFromString};

my ($x, $y, $z) = (0, 0, 0);
my %opts = ('x=i', \$x, 'y=i', \$y, 'z=i', \$z);

dd \%opts;

GetOptions(%opts);

dd \%opts;

print 'Enter new: ';
chomp(my $new = <>);

GetOptionsFromString($new, %opts);

dd \%opts;
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Sample run:

$ pm_1184309_getopt_long_opts_from_string.pl -x 1 -y 2
{ "x=i" => \0, "y=i" => \0, "z=i" => \0 }
{ "x=i" => \1, "y=i" => \2, "z=i" => \0 }
Enter new: -y 3 -z 4 -x 0
{ "x=i" => \0, "y=i" => \3, "z=i" => \4 }
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In "Re^2: How to process Getopt::Long from STDIN", you asked:

"I'm not sure how this works with GetOptionsFromString perhaps?"

That may answer your question. See the Getopt::Long documentation for details.