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But @INC can be altered at run time. Consider that your default @INC is just:

/eg/lib

You run perl -I/eg/custom myscript.pl.

Now @INC is:</c>

/eg/custom /eg/lib

Imagine that myscript.pl contains use mylibs which loads /eg/custom/mylibs.pm. This module itself tinkers with @INC at run-time, adding another path at the front.

/corporate/lib /eg/custom /eg/lib

Now you want to launch another Perl process via system(), so what do you do? Something like:

my @incs = map { "-I$_" } @INC; system($^X, @incs, 'other-script.pl');

So when the other script starts, it will start with this in @INC:

/corporate/lib /eg/custom /eg/lib

Now let's imagine that other-script.pl also does use mylibs. Rather than that loading /eg/custom/mylibs.pm, it might now load /corporate/lib/mylibs.pm, which is perhaps an older version of the mylibs package which behaves differently to how we wanted.

Granted this is a rare situation, but there do exist packages along these lines; packages that exist entirely to manipulate @INC, such as local::lib. Combining these libraries with system($^X) can get you into a merry little pickle.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re^4: Know a perl's -I flag from perl? by tobyink
in thread Read a perl's -I flag from perl? by petr999

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