Engaging beancounter mode ... - ready.

sub test_function {
    my $ref = shift;    # this function takes one argument, a ref to a
+n 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";
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There is an edge case where this code produces a wrong error message:

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

sub test_function {
    my $ref = shift;    # this function takes one argument, a ref to a
+n 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 $@;
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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:\>
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Generally, the error messages are slightly confusing: They report the line where the error was detected, not where the error was made. Carp can help:

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 a
+n 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 $@;
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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:\>
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Doing the same without the stack trace takes a little bit more work.

Alexander