I think you will find that "easiest" will depend on the system you are on, but I would begin by looking at the "User Interfaces" section of Tutorials, which includes tutorials for Tk, Gtk, and wxPerl.

Hope that helps.

Maybe consider https://metacpan.org/pod/distribution/IUP/lib/IUP.pod#GetParam

Like:

perl -MIUP -E '($status, $val) = IUP->GetParam("Title", undef, "String: %s\n", "test"); say $val'

Tk is almast simple when you have understood basic mechanics.

It can run on very different OS and here around is full of examples and even books.

It seems weird to me mixing a cli application with some gui part: in this case use a command line interface like the yet suggested Ask or doing it by hand reading from STDIN

A full Tk application asking the user for some parameter can look like:

use strict;
use warnings;

use Tk;

my $param = '';

my $mw = Tk::MainWindow->new;

$mw->Label(-text=>'Please enter your parameter:')->pack;

$mw->Entry(-textvariable=>\$param)->pack;

$mw->Button(-text=>'Submit (even if no button are needed',
            -command=>sub{
                print "Button was pressed: \$param is now '$param'\n";
            })->pack;

MainLoop();
[download]

Please note that $param is modified while typing in the Entry not when you hit the Submit button.

L*

Curses is arguably the simplest GUI and there are a number of modules available to interface with it.

There is Curses which offers a simple procedural interface and is a very long-standing module. You'll find lots of sample scripts for this on the web, but some will be very old.

For OO there's Curses::UI, but that hasn't seen an update in 5 years and has quite a few outstanding issues.

Plus others I haven't looked at: Curses::Application, Curses::Simp, etc.

I need to make a simple stdin from user in GUI format...

Do you need a Gui? Or would a Cui suffice?

Also: What OS? Or do you need OS agnostic? (If so, explain why?)