I want to capitalize letters that follow colons. Here is the code:

(replace-regexp-in-string ": \w" 'upcase ": really")

The result I expected is : Really. Instead I get : really.

Similarly, this also doesn't work:

(replace-regexp-in-string ": [:alpha:]" 'upcase ": really")

But this works:

(replace-regexp-in-string ": r" 'upcase ": really")

And this, too:

(replace-regexp-in-string ": [:alpha:]" 'upcase ": alright")

My LANG environment variable is set to en_US.UTF-8.

  • 2
    In the first example you are missing a backslash and in the second a set of braces. I.e. these regexps don't match the provided string.
    – politza
    Commented Jan 30, 2015 at 1:09
  • 2
    And I'm pretty sure your last example didn't work ☺
    – Malabarba
    Commented Jan 30, 2015 at 1:42
  • 1
    @Malabarba, there was an error in the example. I fixed it.
    – tmalsburg
    Commented Jan 30, 2015 at 5:42

1 Answer 1


You need to double the backslash in a Lisp string:

(replace-regexp-in-string ": \\w" #'upcase ": really")

See the Elisp manual, node Syntax for Strings.

And a char class has chars inside [], so put [:alpha:] inside [].

(replace-regexp-in-string ": [[:alpha:]]" #'upcase ": really")

See the Elisp manual, node Regexp Special.

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