How can I convert from underscores to camel case with a regex?

Question

How can I convert names with underscores into camel case names as follows using a single Java/Perl regular expression search and replace?

underscore_variable_name -> underscoreVariableName
UNDERSCORE_VARIABLE_NAME -> underscoreVariableName
_LEADING_UNDERSCORE -> leadingUnderscore

The reason I ask for a single regular expressions is that I want to do this using Eclipse or Notepad++ search and replace.

Qtax · Accepted Answer · 2012-03-12T16:16:04.827

30

Some Perl examples:

my $str = 'variable_name, VARIABLE_NAME, _var_x_short,  __variable__name___';

### solution 1
$_ = $str;

$_ = lc;
s/_(\w)/\U$1/g;

say;

### solution 2: multi/leading underscore fix
$_ = $str;

$_ = lc;
s/(?<=[^\W_])_+([^\W_])|_+/\U$1/g;

say;

### solution 3: without prior lc
$_ = $str;

s/(?<=[^\W_])_+([^\W_])|([^\W_]+)|_+/\U$1\L$2/g;

say;

Output:

variableName, variableName, VarXShort,  _variable_name__
variableName, variableName, varXShort,  variableName
variableName, variableName, varXShort,  variableName

edited Mar 12 '12 at 16:16

answered Mar 12 '12 at 15:35

Qtax

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+1: Neat. About the only possible quibble is that `_tea_break` would become `TeaBreak` rather than `teaBreak` or `_teaBreak`. But that would serve someone right for using names starting with an underscore. – Jonathan Leffler Mar 12 '12 at 15:38
@JonathanLeffler, you're right, and there would also be problems if multiple consecutive underscores were used. Updated the answer to fix that. – Qtax Mar 12 '12 at 15:49
1

Thanks, but because this is for use in editor search and replace dialogs I was asking to do this using a single regex. `$_ = lc` breaks this constraint. Can you think of a way to combine them? – Jeff Axelrod Mar 12 '12 at 15:50
@glenviewjeff, the `lc` less solution didn't work right for names like `var_x_short`, updated and fixed now. – Qtax Mar 12 '12 at 16:18
1

Thanks a lot for this answer. You stand next to Jesus in my book. – gran_profaci Jun 27 '13 at 01:06

score 4 · Answer 2 · answered Sep 10 '13 at 12:29

4

Uppercases letters following _-:

s/[_-]([a-z])/\u$1/gr

answered Sep 10 '13 at 12:29

score 2 · Answer 3 · answered Jun 07 '13 at 15:24

If you already have camelCase variables in the string, then @Qtax's answer will make them lowercase. If all of your variables are lower-case under_scored then you can make the following modification to #3: W --> A-Z

's/(?<=[^\A-Z_])_+([^\A-Z_])|([^\A-Z_]+)|_+/\U$1\L$2/g'

score 1 · Answer 4 · answered May 13 '20 at 11:10

1

I prefer user846969's answer but somehow it was not finding other matches in the tool that is using EBNF (extended Backus-Naur form). Here is somthing that worked for me:

/(?:([a-z0-9]*)[_-])([a-z])/${1}${2:/upcase}/g

answered May 13 '20 at 11:10

jaques-sam

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How can I convert from underscores to camel case with a regex?

4 Answers4