use FindBin; use lib "$FindBin::Bin/../lib";
or
use FindBin qw($Bin); use lib "$Bin/../lib";
This allows a user to setup a directory tree for some software with directories <root>/bin and <root>/lib and then the above example will allow the use of modules in the lib directory without knowing where the software tree is installed.
If perl is invoked using the -e option or the perl script is read from STDIN then FindBin sets both $Bin and $RealBin to the current directory.
$Bin - path to bin directory from where script was invoked $Script - basename of script from which perl was invoked $RealBin - $Bin with all links resolved $RealScript - $Script with all links resolved
perl filenameand filename does not have executable rights and a program called filename exists in the users $ENV{PATH} which satisfies both -x and -T then FindBin assumes that it was invoked via the $ENV{PATH}.
Workaround is to invoke perl as
perl ./filename