Find::Lib appears to be exactly that.

use Find::Lib '../lib';
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By the way, you have abs_path (aka realpath) and dirname backwards.

use Cwd            qw( abs_path );
use File::Basename qw( dirname );

use lib dirname(abs_path($0)).'/../lib';
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The order in which you use them will fail if you create a symlink to the script.

Update: Find::Lib touts its handling of symlinks, but it fails to handle a symlink to the script.

$ find ! -type d -exec ls -l {} +
lrwxrwxrwx 1 eric users  8 Feb 22 17:04 ./a.pl -> bin/a.pl
-rwx------ 1 eric users 53 Feb 22 17:04 ./bin/a.pl
-rw------- 1 eric users 16 Feb 22 17:03 ./lib/Mod.pm

$ cat bin/a.pl
#!/usr/bin/env perl
use Find::Lib '../lib';
use Mod;

$ cat lib/Mod.pm
package Mod;
1;

$ bin/a.pl

$ a.pl
Can't locate Mod.pm in @INC (@INC contains: /home/eric/usr/perlbrew/pe
+rls/perl-5.12.2/lib/site_perl/5.12.2/i686-linux /home/eric/usr/perlbr
+ew/perls/perl-5.12.2/lib/site_perl/5.12.2 /home/eric/usr/perlbrew/per
+ls/perl-5.12.2/lib/5.12.2/i686-linux /home/eric/usr/perlbrew/perls/pe
+rl-5.12.2/lib/5.12.2 .) at ./a.pl line 3.
BEGIN failed--compilation aborted at ./a.pl line 3.
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