Perl - Hashes

Hashes - Perl module P211

A hash is a collection of scalars, but each element can be named rather than numbered as it would be in a list. This makes it similar to a database table in many ways and leads to some truly remarkable capabilities.

This topic is presented on public courses Perl Programming, Perl bootcamp

Examples from our training material

account	Sample - extracting statistics from an access log file
acl	Sample answer - web_c2, page 152
bankout	initialising a hash
cbdemo	How sort callbacks work
env2	ENV module to import variables as globals
envrep	use of %ENV
h1	Setting up, adding to, changing a hash (associative array)
hash1.pl	setting up and using a hash
nip2	set up and loop though a hash in various ways
nip3	the danger of jumping out of an each loop
nip4	Sorting the keys of a hash
niports	hash - manipulation
pathit	List out all programs on the current $PATH
peeps.pl	Set up a hash of people
so2	Sort using your own sort subroutine
so4	sort using a more complex routine
so5	sorting with a comparison block
sorter	Demonstration of default dort order
stdhash	keys must be unique - example illustrates the problem
stdhash3	Hash keys must be unique - so make up a new keu
stdhash4	Keys must be unique - design new keys, add accessor loops to find multiple keys
sthash2	Keys must be unique - solution 1 - Append all possible values
ukports	fill and look up a hash
web_count	Sample answer - web access counter question 1
webc2	Sample answer - 2nd question

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from http://www.training-notes.co.uk.

Topics covered in this module

Setting up a hash.
Accessing a hash.
Individual elements.
The whole hash.
Processing every element of a hash.
Keys and values.
Each.
Ordering a hash (sorting).
Sorting using your own subroutine for comparison.
Operators cmp and <=>.
A more complex sort selector routine.
Sorting with a comparison block.
Programming techniques.
Non-unique keys.
Looking for matching keys.
Use hashes for stock numbers.
Deleting elements, clearing out hashes.
Initialising hashes.
Special hashes.
%ENV.
Summary.

Complete learning

If you are looking for a complete course and not just a information on a single subject, visit our Listing and schedule page.

Well House Consultants specialise in training courses in Python, Perl, PHP, and MySQL. We run Private Courses throughout the UK (and beyond for longer courses), and Public Courses at our training centre in Melksham, Wiltshire, England. It's surprisingly cost effective to come on our public courses - even if you live in a different country or continent to us.

We have a technical library of over 600 books on the subjects on which we teach. These books are available for reference at our training centre. Also available is the Opentalk Forum for discussion of technical questions.