BEGIN {
  if (@INC) {
     use lib '/foo';
  } else {
     use lib '/bar';
  }
}
print "INC IS: @INC\n";

##</code><code>##

$ perl begin.pl
INC IS: /bar /foo /usr/local/lib/perl5/5.6.1/i686-linux /usr/local/lib/perl5/5.6.1 /usr/local/lib/perl5/site_perl/5.6.1/i686-linux /usr/local/lib/perl5/site_perl/5.6.1 /usr/local/lib/perl5/site_perl .