Functions
Syntax
We have already learned how to use
built-in functions.
Now let us learn how to define our own functions.
Function Definition
A user-defined function
(or subroutine) has the following structure:
sub subroutine_name {
statement_1;
statement_2;
statement_3;
...
}
You may place subroutines anywhere inside a Perl program, but for clarity
it is recommended to place them at the end of the file.
Function Name
Function names should follow the same rules as
variable names. Namely, they should
begin with a letter, and then they may have
any number of letters, numbers and underscores (_).
You may use in the same program a variable named
$a, another
variable named @a
and
a subroutine named a and they will mean
different things. (Of course, this is confusing and not recommended...)
Function Invocation
To invoke the subroutine from your Perl program, you write the subroutine name
followed by parentheses. This will cause execution of the block of
statements enclosed by the subroutine's definition curly brackets.
subroutine_name ();
Subroutines may also be invoked from within other subroutines.
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