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### 5.6 Posting Styles

All them variables, they make my head swim.

So what if you want a different `Organization` and signature based on what groups you post to? And you post both from your home machine and your work machine, and you want different `From` lines, and so on?

One way to do stuff like that is to write clever hooks that change the variables you need to have changed. That’s a bit boring, so somebody came up with the bright idea of letting the user specify these things in a handy alist. Here’s an example of a `gnus-posting-styles` variable:

    ((".*"
      (signature "Peace and happiness")
      (organization "What me?"))
     ("^comp"
      (signature "Death to everybody"))
     ("comp.emacs.i-love-it"
      (organization "Emacs is it")))

As you might surmise from this example, this alist consists of several styles. Each style will be applicable if the first element “matches”, in some form or other. The entire alist will be iterated over, from the beginning towards the end, and each match will be applied, which means that attributes in later styles that match override the same attributes in earlier matching styles. So ‘`comp.programming.literate`’ will have the ‘`Death to everybody`’ signature and the ‘`What me?`’ `Organization` header.

The first element in each style is called the `match`. If it’s a string, then Gnus will try to regexp match it against the group name. If it is the form `(header match regexp)`, then Gnus will look in the original article for a header whose name is match and compare that regexp. match and regexp are strings. (The original article is the one you are replying or following up to. If you are not composing a reply or a followup, then there is nothing to match against.) If the `match` is a function symbol, that function will be called with no arguments. If it’s a variable symbol, then the variable will be referenced. If it’s a list, then that list will be `eval`ed. In any case, if this returns a non-`nil` value, then the style is said to match.

Each style may contain an arbitrary amount of attributes. Each attribute consists of a `(name value)` pair. In addition, you can also use the `(name :file value)` form or the `(name :value value)` form. Where `:file` signifies value represents a file name and its contents should be used as the attribute value, `:value` signifies value does not represent a file name explicitly. The attribute name can be one of:

- `signature`
- `signature-file`
- `x-face-file`
- `address`, overriding `user-mail-address`
- `name`, overriding `(user-full-name)`
- `body`

Note that the `signature-file` attribute honors the variable `message-signature-directory`.

The attribute name can also be a string or a symbol. In that case, this will be used as a header name, and the value will be inserted in the headers of the article; if the value is `nil`, the header name will be removed. If the attribute name is `eval`, the form is evaluated, and the result is thrown away.

The attribute value can be a string, a function with zero arguments (the return value will be used), a variable (its value will be used) or a list (it will be `eval`ed and the return value will be used). The functions and sexps are called/`eval`ed in the message buffer that is being set up. The headers of the current article are available through the `message-reply-headers` variable, which is a vector of the following headers: number subject from date id references chars lines xref extra.

In the case of a string value, if the `match` is a regular expression, or if it takes the form `(header match regexp)`, a ‘`gnus-match-substitute-replacement`’ is proceed on the value to replace the positional parameters ‘`\n`’ by the corresponding parenthetical matches (see See Replacing the Text that Matched in The Emacs Lisp Reference Manual.)

If you wish to check whether the message you are about to compose is meant to be a news article or a mail message, you can check the values of the `message-news-p` and `message-mail-p` functions.

So here’s a new example:

    (setq gnus-posting-styles
          '((".*"
             (signature-file "~/.signature")
             (name "User Name")
             (x-face-file "~/.xface")
             (x-url (getenv "WWW_HOME"))
             (organization "People's Front Against MWM"))
            ("^rec.humor"
             (signature my-funny-signature-randomizer))
            ((equal (system-name) "gnarly")  ;; A form
             (signature my-quote-randomizer))
            (message-news-p        ;; A function symbol
             (signature my-news-signature))
            (window-system         ;; A value symbol
             ("X-Window-System" (format "%s" window-system)))
            ;; If I’m replying to Larsi, set the Organization header.
            ((header "from" "larsi.*org")
             (Organization "Somewhere, Inc."))
            ;; Reply to a message from the same subaddress the message
            ;; was sent to.
            ((header "x-original-to" "me\\(\\+.+\\)@example.org")
             (address "me\\1@example.org"))
            ((posting-from-work-p) ;; A user defined function
             (signature-file "~/.work-signature")
             (address "user@bar.foo")
             (body "You are fired.\n\nSincerely, your boss.")
             ("X-Message-SMTP-Method" "smtp smtp.example.org 587")
             (organization "Important Work, Inc"))
            ("nnml:.*"
             (From (with-current-buffer gnus-article-buffer
                     (message-fetch-field "to"))))
            ("^nn.+:"
             (signature-file "~/.mail-signature"))))

The ‘`nnml:.*`’ rule means that you use the `To` address as the `From` address in all your outgoing replies, which might be handy if you fill many roles. You may also use `message-alternative-emails` instead. See Message Headers in Message Manual.

Of particular interest in the “work-mail” style is the ‘`X-Message-SMTP-Method`’ header. It specifies how to send the outgoing email. You may want to sent certain emails through certain SMTP servers due to company policies, for instance. See Message Variables in Message Manual.

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