How to replace a character by another in a variable

Question

I want to know if there is a way to replace a character by another in a variable. For example replacing every dots with underscores in a string variable.

Answer 1

I haven't tried it, but based on the Variables specification, the way I'd try to approach this would be to try to match on the text before and after a dot, and then make new variables based on the matches. Something like:

set "value" "abc.def";
if string :matches "${value}" "*.*" {
    set "newvalue" "${1}_${2}
}

This will, of course, only match on a single period because Sieve doesn't include any looping structures. While there's a regex match option, I'm not aware of any regex replacement Sieve extensions.

Another approach to complex mail filtering you can do with Dovecot (if you do need loops and have full access to the mail server) is their Dovecot-specific extensions like vnd.dovecot.pipe which allows the mail administrator to define full programs (written in whatever language one wishes) to process mail on its way through.

Answer 2

Following @BluE's comment, if your use case is to store e-mails in folders per recipient address or something like that, perhaps you don't actually want a generic character replace function but some way to create mailboxes with dots in their names. In the case of dovecot, there seem to be a solution: [Dovecot] . (dot) in maildir folder names

https://wiki2.dovecot.org/Plugins/Listescape

Ensure one of the files in /etc/dovecot/conf.d contains this line:

mail_plugins = listescape

Then you can filter mailing lists into separate boxes based on their IDs.

This Sieve script snippet picks the ID from the x-list-id header:

if exists "x-list-id" {
    if header :regex "x-list-id" "<([\.@a-z_0-9-]+)" {
        set :lower "listname" "${1}";
        fileinto :create "mailing_list\\${listname}";
    } else {
        keep;
    }
    stop;
}