use_perl_534() {
  export PATH="/opt/local/bin:$PATH"
#  export PERL5LIB="/opt/local/lib/perl5/5.34/site_perl:/opt/local/lib/perl5/5.34/lib:$PERL5LIB"
  PERL5LIB="/opt/local/lib/perl5:/opt/local/lib/perl5/5.34:/opt/local/lib/perl5/5.34/darwin-thread-multi-2level:/opt/local/lib/perl5/vendor_perl/5.34:/opt/local/lib/perl5/vendor_perl/5.34/darwin-thread-multi-2level:$PERL5LIB"
  echo "Using Perl 5.34"
}

# /opt/perl/lib/perl5/darwin-2level/ntheory.pm
# /opt/perl/lib/lib/perl5/darwin-2level/ntheory.pm
use_perl_538() {
  export PATH="/opt/perl/bin:$PATH"
#  export PERL5LIB="/opt/local/lib/perl5/5.38/site_perl:/opt/local/lib/perl5/5.38/lib:$PERL5LIB"
  PERL5LIB="/opt/perl/lib/perl5:/opt/perl/lib/perl5/darwin-2level:/opt/perl/lib/perl5/darwin-2level/.meta:/opt/perl/lib/5.38.2:/opt/perl/lib/5.38.2/darwin-2level:/opt/perl/lib/site_perl/5.38.2:/opt/perl/lib/site_perl/5.38.2/darwin-2level:/opt/perl/lib/lib:/opt/perl/lib/lib/perl5:/opt/perl/lib/lib/perl5/darwin-2level:/opt/perl/lib/lib/perl5/darwin-2level/.meta:$PERL5LIB"
  echo "Using Perl 5.38"
}

# /opt/perl_5.40.1/lib/lib/perl5/local
# /opt/perl_5.40.1/lib/lib/perl5/darwin-thread-multi-2level/auto/local
use_perl_540() {
  export PATH="/opt/perl_5.40.1/bin:$PATH"
#  export PERL5LIB="/opt/perl_5.40.1/lib/perl5/site_perl:/opt/perl_5.40.1/lib/perl5:$PERL5LIB"
  PERL5LIB="/opt/perl_5.40.1/lib:/opt/perl_5.40.1/lib/5.40.1:/opt/perl_5.40.1/lib/5.40.1/darwin-2level:/opt/perl_5.40.1/lib/site_p
erl:/opt/perl_5.40.1/lib/site_perl/5.40.1:/opt/perl_5.40.1/lib/site_perl/5.40.1/darwin-2level:/opt/perl_5.40.1/lib/lib:/opt/perl_5
.40.1/lib/lib/perl5:/opt/perl_5.40.1/lib/lib/perl5/darwin-thread-multi-2level:/opt/perl_5.40.1/lib/lib/perl5/darwin-thread-multi-2
level/.meta:$PERL5LIB"
  echo "Using Perl 5.40.1"
}

##</code><code>##

./wagstaff_primes.pl
Can't locate local/lib.pm in @INC (you may need to install the local::lib module) (@INC entries checked: /opt/perl_5.40.1/lib/site_perl/5.40.1/darwin-2level /opt/perl_5.40.1/lib/site_perl/5.40.1 /opt/perl_5.40.1/lib/5.40.1/darwin-2level /opt/perl_5.40.1/lib/5.40.1) at ./wagstaff_primes.pl line 4.
BEGIN failed--compilation aborted at ./wagstaff_primes.pl line 4.

##</code><code>##

find /opt/perl_5.40.1/lib -type f -name lib.pm
/opt/perl_5.40.1/lib/5.40.1/darwin-2level/lib.pm
/opt/perl_5.40.1/lib/lib/perl5/local/lib.pm