Defining subroutines

sub declarations, the parameter signature, and how a value gets returned.

A subroutine is declared with sub, a name, a signature in parentheses, and a body. Calling it binds the arguments to the signature's parameters.

A basic sub #

sub greet($name) {
    "Hello, $name!";
}
say greet("Ada");

Hello, Ada!

Returning a value #

The value of the last expression is returned automatically — no return needed. Use an explicit return to leave early.

sub square($x) {
    $x ** 2;
}
say square(9);

81

return stops the sub immediately; anything after it does not run:

sub double($x) {
    return $x * 2;
    say "never reached";
}
say double(5);

10

Notes #

• The signature ($name) declares one required positional parameter. Parameters are read-only by default — assigning to $name inside the sub is an error unless it is declared is rw or is copy.
• A sub with an empty signature, sub f() { … }, takes no arguments; calling it with any is an error.
• Subs are lexically scoped by default and can be nested inside other subs or blocks.