Perl Language Subroutines Creating subroutines
Example
Subroutines are created by using the keyword sub followed by an identifier and a code block enclosed in braces.
You can access the arguments by using the special variable @_, which contains all arguments as an array.
sub function_name {
my ($arg1, $arg2, @more_args) = @_;
# ...
}
Since the function shift defaults to shifting @_ when used inside a subroutine, it's a common pattern to extract the arguments sequentially into local variables at the beginning of a subroutine:
sub function_name {
my $arg1 = shift;
my $arg2 = shift;
my @more_args = @_;
# ...
}
# emulate named parameters (instead of positional)
sub function_name {
my %args = (arg1 => 'default', @_);
my $arg1 = delete $args{arg1};
my $arg2 = delete $args{arg2};
# ...
}
sub {
my $arg1 = shift;
# ...
}->($arg);
5.20.0
Alternatively, the experimental feature "signatures" can be used to unpack parameters, which are passed by value (not by reference).
use feature "signatures";
sub function_name($arg1, $arg2, @more_args) {
# ...
}
Default values can be used for the parameters.
use feature "signatures";
sub function_name($arg1=1, $arg2=2) {
# ...
}
You can use any expression to give a default value to a parameter – including other parameters.
sub function_name($arg1=1, $arg2=$arg1+1) {
# ...
}
Note that you can't reference parameters which are defined after the current parameter – hence the following code doesn't work quite as expected.
sub function_name($arg1=$arg2, $arg2=1) {
print $arg1; # => <nothing>
print $arg2; # => 1
}
