SUBROUTINES

SUBROUTINES• Thus far we have utilized Perl predefined functions such as print and chomp. However, it is

useful to be able to create our own functions to simplify tasks.

• A subroutine is a user defined function that allows the scripter to:• Organize code

• Recycle code

• Reuse code

• Recall the scope of a function is local; Therefore we must take that into account when developing them if we want global actions.

• Good Programming: Place subroutines below your main script

DEFINING A SUBROUTINE• Perl has simplified the task to define a

function• Question: In other languages how do we

define a function/method?

• Code: sub subName

{

Block;

}

• Common Mistakes: Thinking that subroutines are like functions and placing () at the end of the definition.

• Ex.

use Cwd;

use strict;

my $currPath = getcwd;

sub homeSwitch

{

if ($currPath ne “/u/j/s/jsilver5/”)

{

$currPath = getcwd;

chdir “/u/j/s/jsilver5/”;

}

else

{

chdir $currPath;

}

}

INVOKING/CALLING A SUBROUTINE• In order to call a subroutine use an & followed by the name of the subroutine.• Code: &subName;

• Ex. • &homeSwitch;

• Common Mistakes: Thinking that subroutines are like functions and placing () at the end of the call

MAKE IT WORTHWHILE WITH A RETURN

• Each subroutine calculates a return value upon the completion of the subroutines execution.

• More often than not you will want to store the outcome of the subroutine to be used later in the script, repeatedly, etc.

• Larry thought it was wasteful and required too much effort to determine a difference between void and data type functions that he made all Perl functions return a value.

• Specifically the last calculation performed in a subroutine is stored as the return of the subroutine.

RETURN EXAMPLESQuestion: What is the return value for each of the following?

• Ex 2

my $birthStone = “Diamond”;

my $street = “Patriot”;

sub nameSmush

{

birthStone = $birthstone . “ the “ . $street;

}

print(&nameSmush);

• Ex 3

my $birthStone = “Diamond”;

my $street = “Patriot”;

sub nameSmush

{

$birthStone = $birthstone . “ the “ . $street;

print(“Your superhero name is $birthStone“);

}

$testVar = &nameSmush;

• Ex 1.

my $birthStone = “Diamond”;

my $street = “Patriot”;

sub nameSmush

{

birthStone = $birthstone . “ the “ . $street;

}

&nameSmush;