Elisp: Format string where resulting string contains format characters
reddit / emacs

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pragmat1c1 · 2022-05-10 11:49

I am processing a list of URLs where spaces have been replaced by
"%2F".

For example: "https://example.com/query=aasfasdf%2Fapp%2Fuser=test"

Now I try to create new strings that contain those URLs.

`(format "Name: %s   URL: %s" name url)`

and get an error:

`(error "Not enough arguments for format string")`

Apparently the resulting string contains those "%2F" strings, and
`format` cannot fill them.

Is there a way to provide literal strings to `format` function and
prevent it from trying to interpolate the resulting string?

## Edit: Here is a code fragment that demonstrates it

```
(let ((name "Test URL")
      (url "https://firebasestorage.googleapis.com/v0/b/firescript-
577a2.appspot.com/o/imgs%2Fapp%2FJames%1Qr5z3L.png?alt=media&token=357
1-455b-960f-b68acc31faf0"))
  (message (format "%s %s" name url)))
```

## Solved

https://www.gnu.org/software/emacs/manual/html_node/elisp/Displaying-
Messages.html

```
Warning: If you want to use your own string as a message verbatim,
don’t just write (message string). If string contains ‘%’, ‘`’, or ‘'’
it may be reformatted, with undesirable results. Instead, use (message
"%s" string).
```

So this does the trick:

```
(let ((name "Test URL")
      (url "https://firebasestorage.googleapis.com/v0/b/firescript-
577a2.appspot.com/o/imgs%2Fapp%2FJames%1Qr5z3L.png?alt=media&token=357
1-455b-960f-b68acc31faf0"))
  (message "%s" (format "%s %s" name url)))
```

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usaoc · 2022-05-10 12:55

[`message` accepts a format string as the first argument](https://www.
gnu.org/software/emacs/manual/html_node/elisp/Displaying-
Messages.html).  [It uses `format-message` under the
hood](https://github.com/emacs-mirror/emacs/blob/145727df29d2e067b062c
b44548dd97b076567fa/src/editfns.c#L2849), [which see](https://www.gnu.
org/software/emacs/manual/html_node/elisp/Formatting-Strings.html).
Therefore, `(message "%s %s" name url)` is enough.

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pragmat1c1 · 2022-05-10 18:29

Excellent! Thank you.