sub test_function {
    my $ref = shift;    # this function takes one argument, a ref to an ARRAY

    # Note: you could do extra manual checking of function arguments.
    # Not necessarily recommended: shown for educational purposes.
    defined($ref) or die "oops: you did not pass any arguments";
    @_ and die "oops: this function takes exactly one argument";

##</code><code>##

use strict;
use warnings;
use feature 'say';

sub test_function {
    my $ref = shift;    # this function takes one argument, a ref to an ARRAY

    # Note: you could do extra manual checking of function arguments.
    # Not necessarily recommended: shown for educational purposes.
    defined($ref) or die "oops: you did not pass any arguments";
    @_ and die "oops: this function takes exactly one argument";
}

say "Calling test_function with no arguments:";
eval { 
    test_function();
};
say $@;

say "Calling test_function with a single undefined argument:";
eval {
   test_function(undef);
};
say $@;

##</code><code>##

X:\>perl foo.pl
Calling test_function with no arguments:
oops: you did not pass any arguments at foo.pl line 10.

Calling test_function with a single undefined argument:
oops: you did not pass any arguments at foo.pl line 10.


X:\>

##</code><code>##

use strict;
use warnings;
use feature 'say';
use Carp qw( croak );

sub test_function {
    @_==1 or croak "oops: this function takes exactly one argument";
    my $ref = shift;    # this function takes one argument, a ref to an ARRAY

    # Note: you could do extra manual checking of function arguments.
    # Not necessarily recommended: shown for educational purposes.
    defined($ref) or croak "oops: argument is not defined";
}

say "Calling test_function with no arguments:";
eval { 
    test_function();
};
say $@;

say "Calling test_function with an undefined argument:";
eval {
   test_function(undef);
};
say $@;

##</code><code>##

X:\>perl foo.pl
Calling test_function with no arguments:
oops: this function takes exactly one argument at foo.pl line 7
        main::test_function() called at foo.pl line 17
        eval {...} called at foo.pl line 16

Calling test_function with an undefined argument:
oops: argument is not defined at foo.pl line 12
        main::test_function(undef) called at foo.pl line 23
        eval {...} called at foo.pl line 22


X:\>