Programming Perl, 4th Edition

lib

use lib "$ENV{HOME}/libperl";   # add ~/libperl
no lib ".";                     # remove cwd

This pragma simplifies the manipulation of @INC at compile time. It is typically used to add extra directories to Perl’s search path so that later do, require, and use statements will find library files that aren’t located in Perl’s default search path. It’s especially important with use, since that happens at compile time, too, and setting @INC normally (that is, at runtime) would be too late.

Parameters to use lib are prepended to the beginning of Perl’s search path. Saying use lib LIST is almost the same as saying BEGIN { unshift(@INC, LIST) }, but use lib LIST includes support for platform-specific directories. For each given directory $dir in its argument list, the lib pragma also checks to see whether a directory named $dir/$archname/auto exists. If so, the $dir/$archname directory is assumed to be a corresponding platform-specific directory, so it is added to @INC (in front of $dir).

To avoid redundant additions that slow access time and waste a small amount of memory, trailing duplicate entries in @INC are removed when entries are added.

Normally, you should only add directories to @INC. If you do need to delete directories from @INC, take care to delete only those that you yourself added, or those you’re somehow certain aren’t needed by other modules in your program. Other modules may have added directories to your @INC that they need for correct operation.

The no lib pragma deletes all instances of each ...