1. PERL: part II hashes, foreach control statements, and the split function
By: Kevin Walton

2. Hashes
Hashes are similar to arrays, but use strings instead of numbers for indexing.
Very similar to Maps in C++
All hash variables start with the character “%”
%numbers = (“first”,”1”,”second”,”2”,”third”,”3”)
Key
Value
“first” 1
“second” 2
“third” 3

3. Hash Commands
“reverse” – changes keys into values and values into keys
“keys” – returns an array of keys
“values” – returns an array of values
EX: %inverse_hash=reverse %numbers;
Hash %numbers gets reversed, keys become values and values become keys.
After reversing the hash is assigned to another variable %inverse_hash;

4. Each Function EX: while (($name, $address) = each %addressbook)
{ print "$name lives at $address\n"; }
Each successive key-value pair is returned by function each, and assigned to variables $name and $address and then printed out.
The each function allows for easy extraction of data from entire hashes

5. Foreach Control Structure
Foreach works like the each function, only with arrays instead of hashes
EX: foreach $word
{ print "$word\n"; }
Variable $word takes the successive values All elements of the list are printed in order.

6. Split Function
The “split” function breaks up a string and places it into an array.
The function uses a regular expression to divide the string
Works on the $_ variable unless otherwise specified.

7. Split Example
$info = “Kevin,Walton,Student,19,Race = split(/,/, $info);
Split breaks up the $info string so that:
@personal = (“Kevin”, “Walton”, “Student”, “19”, “Race Street”);

8. Regular Expressions Regular expressions can be used with split
EX: $_ = “Capes:Geoff::Shot putter:::Big Avenue“
@personal = split(/:+/);
The string is split at any point the program encounters one or more colons