BEGIN{($path = $0) =~ s[[\\/][^\\/]+$][];}
BEGIN{ use lib $path;}
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use implies BEGIN, so that BEGIN should not be needed.

There is a simpler way: use lib do { ... }, shown in Re^2: Calculations before using lib;. Combined with the s///r syntax from newer perls, this can be collapsed to use lib do { $0=~s[[\\/][^\\/]+$][]r };.

Also note that $0 may not always contain an absolute path:

>cat tmp.pl
#!/usr/bin/perl
use strict;
use warnings;
print "$0\n";

>chmod +x tmp.pl
>perl tmp.pl
tmp.pl
>perl ./tmp.pl
./tmp.pl
>perl /tmp/tmp.pl
/tmp/tmp.pl
>./tmp.pl
./tmp.pl
>tmp.pl
./tmp.pl
>
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Alexander