You don't specify in which environment you are working, so I just presume you work in Perl's native environment UNIX, and that you are using X-windows as your GUI environment. (If you happen to work in a different environment, you've wasted a lot of time, time I can't spend answering other peoples questions.)

#!/usr/bin/perl

use strict;
use warnings;

my $pid = fork err die "Failed to fork: $!";

unless ($pid) {
    exec "xterm" or die "Failed to exec: $!";
}
    
    
# $pid is the PID of 'xterm', but we want the PID of the shell
# that's run by the xterm.
# First we need to give the child time to spawn the shell.
sleep 1;
my $shell_pid;
open my $ps => "ps -ef |" or die "Failed to open pipe: $!\n";
while (<$ps>) {
    my ($uid, $proc_pid, $proc_ppid) = split;
    if ($proc_ppid && $proc_ppid eq $pid) {
        $shell_pid = $proc_pid;
        last;
    }
}

# Open the pseudo-terminal of the shell, and print something.
open my $fh => "> /proc/$shell_pid/fd/1" or die "Failed to open termin
+al: $!";
print $fh "Hello!\n";
close $fh;

__END__
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Abigail