dynamically expand @INC beyond BEGIN

somekindafreak has asked for the wisdom of the Perl Monks concerning the following question:

I've read threads 19327 and 272402 that explain that expanding @INC within the code must be done in a BEGIN block. However I want to run some simple menus where the user selects one of multiple release directories (each with a plethora of scripts and modules for that release) and loads just one. Basically saying:

# a menu or two where the user makes a selections that lead up to defi
+ning $lib and $module
unshift(@INC, $lib);     # done mid-execution, after the menu routines
require "$module.pm";    # one clean import that loads a number of oth
+ers all relative to $lib
MODULE::main(@args);     # execute a sub within the one of the newly i
+mported modules within the selected lib
[download]

Is there any way to add a directory to the @INC path using a $variable and done after the BEGIN block? The only thing I can think of is a messy script-that-calls-a-script method that calls the menu routines first, then a second program with $lib and $module passed as args or some other fashion where they can be properly recognized in the BEGIN block.

Comment on dynamically expand @INC beyond BEGIN Download Code

Replies are listed 'Best First'.
Re: dynamically expand @INC beyond BEGIN by JavaFan (Canon) on Apr 16, 2012 at 22:41 UTC
One can modify @INC any time one pleases. Whether it's in a BEGIN block, or outside of it. However, for perl to find a module, the directory the module is to be found in should be added before perl goes looking for it. Considering that `use` is done at compile time, using a `BEGIN` (one which preceeds the `use`) is a simple way of enforcing `@INC` to be set in time. Using `require` and postponing the use of a module to run time, obviously works as well. Doesn't the snippet you gave work?	[reply] [d/l] [select]
Re^2: dynamically expand @INC beyond BEGIN by somekindafreak (Acolyte) on Apr 17, 2012 at 01:52 UTC
feeling stupid at the moment. All morning it was continually saying cannot find MODULE.pm in <@INC_DIRS>, with the front dir being the one loaded that has the module in it. I couldn't figure why it would work when defined in the BEGIN block, but not in my code body and thought it had to be something to do with perl/@INC. Tried it one more time in the body and now it's working just fine. No idea what I had wrong there previously. Thanks for your help.	[reply]
Re^3: dynamically expand @INC beyond BEGIN by ikegami (Patriarch) on Apr 17, 2012 at 04:22 UTC
Note that `require "$lib/Module.pm"` would also have worked if `$lib` contains an absolute directory (and probably even if it doesn't?) You could also make the change to `@INC` temporary using `local @INC = ( $lib, @INC );`.	[reply] [d/l] [select]
Re^4: dynamically expand @INC beyond BEGIN by somekindafreak (Acolyte) on Apr 17, 2012 at 20:20 UTC
Re: dynamically expand @INC beyond BEGIN by Anonymous Monk on Apr 17, 2012 at 13:27 UTC
Also, can you not use `use lib`?	[reply]
Re^2: dynamically expand @INC beyond BEGIN by Anonymous Monk on Apr 17, 2012 at 20:14 UTC
both $lib and $module are variables. use does not work with $vars in any way afaik.	[reply]
Re^3: dynamically expand @INC beyond BEGIN by tobyink (Canon) on Apr 17, 2012 at 22:02 UTC
`# Here's a variable... my $lib; # Make sure it gets defined at compile-time... BEGIN { $lib = '/foo' } # Use the variable in a "use" line... use lib $lib; # Check that it worked... use Data::Dumper; print Dumper \@INC;` [download] ... And lo and behold, it has worked! `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l]