Colored string in mode line

Question

I have:

(setq mode-line-end-spaces "string")

That displays string in the mode-line.
How can I get string in red there?

score 4 · Answer 1 · answered Jul 23 '20 at 16:17

4

@NickD provided a good answer: use a face.

OP's comment to Nick's answer says that he'll try to write a function that, given a string, returns a propertized string. Such functions already exist: propertize does that, and so does add-face-text-property.

For example:

(setq ss  (propertize "abcde" 'face '(:foreground "red")))

or

(setq ss  "abcde")
(add-face-text-property 0 (length ss) '(:foreground "red") nil ss)

answered Jul 23 '20 at 16:17

Drew

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That's good to know. Thanks. – Gabriele Jul 23 '20 at 21:08
You should not try to modify a literal string: (setq ss (copy-sequence "abcde")). – Jul 25 '20 at 11:42
@Fólkvangr: Depends on what behavior you want. Do you want to modify a copy of the original string or the original string? The example of using a literal string here is also for brevity - who knows where the actual original string comes from? But if the intention is to modify the original string, then you don't want to use copy-sequence. – Drew Jul 25 '20 at 16:15
@Drew: copy-sequence allows to create a mutable string (c.f. Elisp manual version 27, section 2.9 Mutability). In your sample code, add-face-text-property modifies a literal string. – Jul 25 '20 at 17:19
@Fólkvangr: Yes, I know. And? If you can modify something then it's mutable. But all of this is extraneous. If you prefer, read "Suppose that the value of ss is a string", instead of the setq. The point of the answer is that you can use add-face-text-property to add color to a string. – Drew Jul 25 '20 at 18:15

NickD · Accepted Answer · 2020-07-27T19:03:35.123

3

You need to create a string with the appropriate face. You do that by attaching a face text property to the string, giving it value of some face (predefined or defined for the specific purpose - you can look at all the predefined faces with M-x list-faces-display and pick one from there, or you can define your own face). E.g. here's a snippet to use a predefined face:

(setq s (copy-sequence "sring"))
(put-text-property 0 6 'face 'custom-invalid s)
(setq mode-line-end-spaces s)

edited Jul 27 '20 at 19:03

answered Jul 23 '20 at 13:57

NickD

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I understand. To generalize your answer, I'll try to write a function that, given a string, returns a propertized string. – Gabriele Jul 23 '20 at 14:02
You should not try to modify a constant string: (setq s (copy-sequence "string")). – Jul 25 '20 at 11:43
OK - edited. Here are some links to provide some context: When to use quote for lists? Modifying quoted lists in Elisp and Which Lisp objects are byte-compiled? plus a similar complaint by @Fólkvangr on an answer of mine that I have not fixed. – NickD Jul 27 '20 at 19:03

Colored string in mode line

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