You seem to want to update PERL5LIB with some paths if they are not there already. But your bash code is too far away from achieving this and it seems easier in Perl e.g.:

#/bin/sh
# ...
export PERL5LIB=`perl -e '
    use strict; use warnings;
    my @addinc = ("/usr/local/lib/perl5/site_perl",
                  "/Users/me/perl/perl_lib"
                 );
    my %inc = map { $_, 1 } split (/\:/, $ENV{PERL5LIB});

    for (@addinc) { # this was just updated
        $inc{$_} or print "$_:";
    }
    print "$ENV{PERL5LIB}\n";
'`
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