Subroutines
- 1. SUBROUTINES
- 2. 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
- 3. 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; } }
- 4. 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
- 5. 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.
- 6. RETURN EXAMPLES Question: 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;