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Convert camelCase to underscores (camel_case)

Terminal - Convert camelCase to underscores (camel_case)
sed -r 's/([a-z]+)([A-Z][a-z]+)/\1_\l\2/g' file.txt
2009-04-28 22:44:45
User: atoponce
Functions: sed
Convert camelCase to underscores (camel_case)

Useful for switching over someone else's coding style who uses camelCase notation to your style using all lowercase with underscores.


There are 3 alternatives - vote for the best!

Terminal - Alternatives

Know a better way?

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What others think

A great one. Thanks.

You missed the underscore though, this should be:

sed -r 's/([a-z]+)([A-Z][a-z]+)/\1_\l\2/g' file.txt

Comment by AmirWatad 286 weeks and 2 days ago

Fixed. I had it in the sample output, but must have missed it in the command itself. Thanks.

Comment by atoponce 286 weeks and 2 days ago

Good job

Comment by kaedenn 286 weeks and 2 days ago

Where's the reverse? :-)

Comment by furicle 286 weeks and 2 days ago

btw, it's good for names like camelCase, but not for camelCaseLong


Comment by AmirWatad 286 weeks and 2 days ago

I think this is a little more robust:

It converts CamelCaseWord or camelCaseWord to camel_case_word (the last pipe is needed to handle the CamelCaseWord case)

sed 's/\([A-Z]\)/_\l\1/g' file.txt | sed 's/^_\([a-z]\)/\1/g'

Comment by AmirWatad 286 weeks and 2 days ago

and this is the reverse:

camel_case_word to camelCaseWord:

sed 's/_\([a-z]\)/\u\1/g' file.txt

camel_case_word to CamelCaseWord

sed 's/_\([a-z]\)/\u\1/g' file.txt | sed 's/^\([a-z]\)/\u\1/g'

Comment by AmirWatad 286 weeks and 2 days ago




The exports above fix a problem where [a-z] is case-insensitive

Here's an explanation from the sed man page (Gnu Sed 4)

[a-z] is case insensitive

You are encountering problems with locales. POSIX mandates that [a-z] uses the current locale's collation order - in C parlance, that means using strcoll(3) instead of strcmp(3). Some locales have a case-insensitive collation order, others don't.

Another problem is that [a-z] tries to use collation symbols. This only happens if you are on the GNU system, using GNU libc's regular expression matcher instead of compiling the one supplied with GNU sed. In a Danish locale, for example, the regular expression ^[a-z]$ matches the string `aa', because this is a single collating symbol that comes after `a' and before `b'; `ll' behaves similarly in Spanish locales, or `ij' in Dutch locales.

To work around these problems, which may cause bugs in shell scripts, set the LC_COLLATE and LC_CTYPE environment variables to `C'.

Here's an example of a line that was having problems due to the case-insensitive problem. Exporting LC_COLLATE and LC_CTYPES fixed the problem. It has to be done each time you log in though. I'm hesitant to put this export into my .profile, as I'm not sure what it will do to the rest of the system programs.

sed -r 's/([a-z]+)([A-Z][a-z]+)/\1_\l\2/g' invalid_name2.txt
Comment by Christian_Long 226 weeks and 1 day ago

sed -r 's/([^A-Z-])([A-Z])/\1_\2/g' file.txt

Replace CamelCaseWord by Camel_Case_Word

Comment by franek 209 weeks ago

Your point of view

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