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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Where do Perl modules load from

When you're writing a Perl program, you're strongly encouraged to use existing code that's already been written to perform common functions. Not only does this save you time re-coding, but it also means you get code that's already tested and proven, and there's only one piece of code to be maintained for each piece of functionallity thereafter rather than two.

Shared (re-used) code may come as part of the Perl distribution - modules like Carp and File::Compare. It may be more specialist code that you download from the CPAN - for example DBI and DBD. Or it may be code that's just shared within your organisation or even just your department or between your personal applications. And in all cases, you "pull" the code into your program with a use statement:

use Carp;
use File::Compare;
use toothbrush;


Where does your Perl program load these modules from? It uses the list @INC which is prepopulated with each of the directories where Perl should look in turn. If you want to add some directories from the command line too, you can use the -I option to perl (see man perlrun for details. But what if you want to add an extra directory or two in your program? You're allowed to change @INC right enough, but even if you do so ahead of your use statement you'll be too late because the use is interpretted at compile time.

Solution? Modify your @INC list in a BEGIN block, since BEGIN blocks are interpretted at compile time too. Here's an example:

BEGIN {
push @INC,"extrabitz";
}

use toothbrush;


The directory "extrabitz" (a subdirectory of the current directory when the program is run) is added onto the end of the list of places for Perl to look ... and in this case, that's probably where it will find "toothbrush".

And if you even wonder what your Perl program has loaded from where, the information is available to you in the %INC hash. Perhaps that should be another day's story!


(written 2005-06-24, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P219 - Perl - Libraries and Resources
  [86] Talk review - Idiomatic Perl, David Cross - (2004-10-12)
  [112] Avoid the wheel being re-invented by using Perl modules - (2004-11-08)
  [358] Use standard Perl modules - (2005-06-25)
  [712] Why reinvent the wheel - (2006-05-06)
  [737] Coloured text in a terminal from Perl - (2006-05-29)
  [760] Self help in Perl - (2006-06-14)
  [1219] Judging the quality of contributed Perl code - (2007-06-06)
  [1235] Outputting numbers as words - MySQL with Perl or PHP - (2007-06-17)
  [1391] Ordnance Survey Grid Reference to Latitude / Longitude - (2007-10-14)
  [1444] Using English can slow you right down! - (2007-11-25)
  [1863] About dieing and exiting in Perl - (2008-11-01)
  [1865] Debugging and Data::Dumper in Perl - (2008-11-02)
  [2229] Do not re-invent the wheel - use a Perl module - (2009-06-11)
  [2234] Loading external code into Perl from a nonstandard directory - (2009-06-12)
  [2427] Operator overloading - redefining addition and other Perl tricks - (2009-09-27)
  [2931] Syncronise - software, trains, and buses. Please! - (2010-08-22)
  [3009] Expect in Perl - a short explanation and a practical example - (2010-10-22)
  [3101] The week before Christmas - (2010-12-23)
  [3377] What do I mean when I add things in Perl? - (2011-08-02)

P209 - Subroutines in Perl
  [96] Variable Scope - (2004-10-22)
  [308] Call by name v call by value - (2005-05-11)
  [531] Packages in packages in Perl - (2005-12-16)
  [588] Changing @INC - where Perl loads its modules - (2006-02-02)
  [775] Do not duplicate your code - (2006-06-23)
  [969] Perl - $_ and @_ - (2006-12-07)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [1202] Returning multiple values from a function (Perl, PHP, Python) - (2007-05-24)
  [1782] Calling procs in Tcl and how it compares to Perl - (2008-09-02)
  [1784] Global - Tcl, PHP, Python - (2008-09-03)
  [1826] Perl - Subs, Chop v Chomp, => v , - (2008-10-08)
  [1850] Daisy the Cow and a Pint of Ginger Beer - (2008-10-21)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1921] Romeo and Julie - (2008-12-04)
  [2069] Efficient calls to subs in Perl - avoid duplication, gain speed - (2009-03-07)
  [2550] Do not copy and paste code - there are much better ways - (2009-12-26)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [2929] Passing a variable number of parameters in to a function / method - (2010-08-20)
  [3066] Separating groups of variables into namespaces - (2010-11-24)
  [3574] Perl functions such as chop change their input parameters - (2012-01-10)
  [3833] Learning to use existing classes in Perl - (2012-08-10)


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Binary Large Objects or bars
Spring turns to Summer
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Context in Perl
Ballooning from Bath
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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