As perl needs to know the arguments for use lib before calling lib's import method, every expression used there is implicitly in a BEGIN block equivalent. So I often use a construct like this in my code:

#!/usr/bin/perl
use strict;
use warnings;
use FindBin ();
use lib do { (my $dir=$FindBin::Bin)=~s|/foo/|/bar/|; $dir };
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This can also be used with taint mode to untaint the value of $FindBin::Bin:

#!/usr/bin/perl -T
use strict;
use warnings;
use FindBin ();
use lib do { $FindBin::Bin=~m|^(/.*)| or die "Can't find myself"; "$1/
+../lib" };
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Alexander