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Changing @INC - where Perl loads its modules

Where does Perl load modules from in its use and require statements? It loads them from directorys in a special list called @INC, from files with a .pm extension in those directorys.

When Perl's installed, @INC is set to a list of directorys that includes generic locations for its standard modules, some release specific directories, and "." the current directory, which are checked in order each time you do a use or require.

Some ways to modify @INC

** You can add to the list in @INC by using the -I command line option:
perl -I /Users/grahamellis/jan06 i2
says "run the perl program i2, additionally checking the jan06 directory for modules"

** You can add to the list within your program by doing so in a BEGIN block prior to the use statements:
BEGIN {
push @INC,"/Users/grahamellis/jan06";
}
use demo;
print "hello world";

Rather curiously, use calls are run at compile time not at run time ... but then so are BEGIN blocks ... so you put your manipulation of @INC into one of those to get it to happen early enough.

** You can add to the beginning of the list by setting the PERL5LIB environment variable prior to running your program:
export PERL5LIB=/Users/grahamellis/jan06
and you can use a colon separated list for that if you want to pre-pend more than one directory.


Footnote - don't you just love Perl's "There's more than one way to do it". Thanks to Dave Cross - author of various Perl books - for reminding me of use lib; - see the comments he's added for a description of this in his own words
(written 2006-02-02, updated 2006-06-05)

Commentatorsays ...
Dave Cross:There is also the "use lib" pragma - this is probably the most common approach. And $PERL5LIB can also be called just $PERLLIB.
(comment added 2006-02-02 06:43:36)
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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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Comment: "Might be worth pointing out -I is capital i not lowercase L ..."
Visitor Ranking 4.0 (5=excellent, 1=poor)

Comment by Marc Flamank (published 2011-01-16)
Might be worth pointing out -I is capital i not lowercase L [#3841]

Comment by Lael Daire (published 2010-03-04)
I wanted to have my main program in a base directory, and the modules in a subdir. Based off your example, I ended up making this:

BEGIN {
@cmd = split(/\//,$0); # gets the program path
pop @cmd; # strips the program name
$libpath = join("\/",@cmd)."/modulelib"; # appends module subdirectory
unshift(@INC,$libpath); # puts modulelib as the first directory to search
}

It worked nicely in my ActivePerl environment and AIX environment. [#3479]

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