Perl - Advanced

1. Perl - Advanced More Advanced Perl • Functions • Control Structures • Filehandles • Process Management

2. Perl Functions • Function – Sub routine Definition • Keyword “sub” – Definition of a sub routine • Name of the routine “subname” • Block Of statements {…} sub subname { statement_1; statement_2; statement_3; }

3. Invoking a User Function • We invoke a user function from within an expression by following the subroutine name with parentheses. • say_what(); or • &say_what(); • A subroutine can invoke another subroutine, and that subroutine can in turn invoke another subroutine, and so on.

4. Return Values

5. Example on Arguments sub add { $sum = 0; # initialize the sum foreach $_ (@_) { $sum += $_; # add each element } return $sum; # last expression evaluated: sum of all elements } • We invoke the above function by typing add($a, $b, …) where inside the parentheses we put as many variables as we like. • The @_ variable is privateto the subroutine. This also means that a subroutine can pass arguments to another subroutine without fear of losing its own @_ variable; The nested subroutine invocation gets its own @_ in the same way.

6. Control Structures

7. Examples of true and false interpretations

8. Control Structures

9. Control Structures

10. Control Structures

11. Control Structures

12. Filehandles

13. Filehandles

14. Filehandles example

15. Process Management

16. Using Processes as Filehandles

17. Using Processes as Filehandles

18. Summary of Process Operations

19. Perl versus C

20. Exercises