1 PERL Functions

2 Functions Functions also called subroutines are “free flowing”. The returned value from a function can be interpreted in many different ways. Anatomy of a subroutine sub subroutineName { my # arguments are passed is the argument stack, the arguments passed &callSub2; # Calling another subroutine return # returning values. #An explicit return is not necessary, by default, the value of the # last expression is returned. } Calling Functions: $result = &subroutine $result = subroutine $result = subroutine; $result = $result = subroutine ();

3 Functions sub showArgs { $first = shift; print "$first \n"; $second = print "$second \n"; $third = shift; print "$third print } showArgs (“A”,”B”,”C”,”D”,”E”); Output: A E B C D

4 sub changeToCaps { my ($line) = $_[0]; $line =~ tr/a-z/A-Z/; return $line; } $text = "this is a test"; $text = &changeToCaps ($text); print $text; print "\n";

5 Scope of variables Global variables are declared outside of any subroutine or function and can be accessed by any part of perl program. Local variables are private to the subroutine in which they are declared. Are of two types: –Dynamic variables are defined with local keyword and are visible to any subroutines called within the subroutine in which they are declared. –Lexical variables are private variables and are seen only in the subroutine in which they are declared. They are declared with keyword my.

6 Functions $global = 100; sub one{ local $bush = "rose"; my $tree = "cherry"; two ($tree); return ++$global; } sub two { my $shrub = $bush; print $shrub; print "\n"; my $a = print "\n"; } &one; #output rose cherry

7 $one = 1234; $two = 6789; $three = 0011; $best = &Max($one,$two,$three ); print $best, "\n"; output: 6789 sub max { my $max = shift foreach $val $max = $val if $val > $max;} return $max; }

8 Functions sub fun3 { $filename = open (FHANDLE,$filename) || die "can't open the file\n"; #all the lines in the # file are copied into # the array, = ; } sub four ($$){ my ($n1,$n2) = ($_[0],$_[1]); my $sum = $n1 + $n2; return $sum; }

9 References Creating References: Examples: $data = “abc”; $a_ref = \$data;#stores the address of data in = (“one”,”two”,”three”); $b_ref = %hash = (“Mon” =>2,”Tue” => 3); $c_ref = \%hash;

10 De-referencing print $$a_ref;or print ${a_ref}; print $$b_ref[1]; or print ${b_ref}[1]; or $b_ref->[1]; print Print $$c_ref{“Mon”}; or print $c_ref->{“Mon”}; or

11 Passing References sub fun4 { my ($array1,$array2) print print = = (5,6,7); fun4 #Rewrite the function to switch arrays sub six{ my ($hashRef1) my %returnHash = (); foreach $key (keys %$hashRef1){ $returnHash{$key} = $hashRef1->{$key}; } return %returnHash; } %fruits = ("A"=>"apple","B"=>"Banana"); %retFruits = six(\%fruits);

12 Some Useful Functions Split Takes scalars and breaks them into arrays. Takes either a delimiter or a regular expression and divides the scalar on that boundary. Example 1: $line = "John Smith"; ($firstName,$lastName) = split / /,$line; print $firstName; print "\n"; print $lastName; Example 2: $line = = split (",",$line); print Example 3: $line = "A,,B,,,C"; #extra = split (",",$line); print # A B C. Example 4: $ line = = split (m",+",$line); print #A B C

13 Some Useful Functions join: joins separate strings into a single string separated by a delimiter. $fullName = join ',',$lastName,$firstName; push: Adds a list to the end of the = = ("D","E","F"); push print #A B C D E F Pop: Returns the last element of the array. $element = print $element;# F shift: Returns the first element of the array $element = print $element;# A unshift: Prepends a list to the front of the = ("X","Y","Z"); unshift print # X Y Z B C D E