-t  Filehandle is opened to a tty.

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use feature qw( say );
use File::Basename;

my $iam = basename($0);

if (-t *STDIN) {
    my $nargs = @ARGV;
    say "Script '$iam' called from a terminal with $nargs arg(s):";
    for (my $idx = 0; $idx < $nargs; $idx++) {
        printf "  %2d.  %s\n", $idx+1, $ARGV[$idx];
    }
} else {
    say "Script '$iam' is receiving input from a pipe";
}

##</code><code>##

Script 'script' called from a terminal with 3 arg(s):
   1.  arg1
   2.  arg2
   3.  arg3

##</code><code>##

Script 'script' is receiving input from a pipe

##</code><code>##

    while (<STDIN>) {
        say "Got input:  $_";
    }