When i need this i use https://metacpan.org/pod/MIME::Base64. As in

use MIME::Base64;
$buf='Authorization: Basic '.encode_base64($args{user}.':'.$args{passw
+ord},'');
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well, yes I could manually do it myself but was hoping I could to this within the LDIF module since all I'm doing is 'read entry -> remove unneeded attributes -> write entry' and not touching most of the attributes in the entry.

with that attribute encrypted

Note that Base64 is not encryption, it is just obfuscation. To anyone who knows what Base64 is, reading the userPassword attribute will be no problem at all whether it's encoded or not.

Anyway, the Net::LDAP::LDIF constructor mentions a encode => 'base64' parameter, have you tried that? It's always best if you show some short but representative code - see SSCCE.

Sorry, "encryption" was not what I meant, but "encoded". Here's example code:

use Net::LDAP::LDIF;
our $old_ldif = Net::LDAP::LDIF->new( "dump.ldif", "r", onerror => 'un
+def' );
our $new_ldif = Net::LDAP::LDIF->new( "dump_new.ldif", "w", onerror =>
+ 'undef', wrap => 76, encode => 'base64' );
while (not $old_ldif->eof()) {
    my $entry = $old_ldif->read_entry();
    if ($old_ldif->error()) {
        warn "Error msg: ", $old_ldif->error(), "\n";
        warn "Error lines:\n", $old_ldif->error_lines(), "\n";
    } else {
        # delete attributes no longer needed
        foreach my $a ($entry->attributes()) {
            if ($a =~ /^attrMatch/) {
                $entry->delete($a);
            }
        }
        $new_ldif->write_entry($entry);
    }
}
$old_ldif->done();
$new_ldif->done();
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Assuming userPassword is not the attribute to remove, I would expect a diff between dump.ldap and dump_new.ldap to only show the attribute(s) that were deleted. But in dump.ldif (from an OpenLDAP slapcat command) the userPassword field is base64 encoded. In the dump_new.ldif file, it's not base64 encoded. Makes the diff harder to read... nothing incorrect with either version though.

At the moment, I don't see anything in the documentation that mentions how to encode individual attributes and not others. Could you also provide a sample LDIF file (anonymized but representative of the original) so that we have something to play with?