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For instance, I want to convert "CamelCasedName" to "camel_cased_name". Is there a way to do this in emacs?

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4  
The short answer to any question of the form "Is there any way to _____ in emacs?" is Always "YES" – Brian Postow Apr 9 '10 at 21:33
up vote 4 down vote accepted

This small bit of code from this page, with a wrapper function and an underscore replacing the hyphen with an underscore, could easily be turned into a command to do that. (Check that it treats leading caps to suit you):

Sample EmacsLisp code to un-CamelCase a string (from http://www.friendsnippets.com/snippet/101/):

(defun un-camelcase-string (s &optional sep start)
  "Convert CamelCase string S to lower case with word separator SEP.
Default for SEP is a hyphen \"-\".

If third argument START is non-nil, convert words after that
index in STRING."
  (let ((case-fold-search nil))
    (while (string-match "[A-Z]" s (or start 1))
      (setq s (replace-match (concat (or sep "-") 
                                             (downcase (match-string 0 s))) 
                                     t nil s)))
    (downcase s)))
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Emacs has glasses-mode which displays camelcase names with underscores in between. (See also http://www.emacswiki.org/emacs/GlassesMode).

If you want to actually change the text of the file M-x query-replace-regexp is probably suitable.

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Moritz Bunkus wrote an elisp function to toggle between CamelCase and c_style

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the package string-inflection is more complete now: github.com/akicho8/string-inflection (note that there's also string-inflection-camelize-lower to change hello_world to helloWorld). – Ehvince May 7 '14 at 12:42

For display purposes only, you can use this:

M-x glasses-mode

If you want a script which actually converts the text, I imagine you'd have to write some elisp. That question is better asked on stack overflow.

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I was able to do this across a whole file quickly with just a query replace regexp.

The search pattern is \([a-z]+\)\([A-Z]\)\([a-z]+\) and the replacement is \1_\,(downcase \2)\3.

The replacement pattern uses elisp right in the pattern. This requires Emacs 22 or later.

In emacs documentation style:

M-C-% \([a-z]+\)\([A-Z]\)\([a-z]+\) RET \1_\,(downcase \2)\3
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