How to remove underscore and capitalize the next character in the first word?

Question

I want to modify the first word of each line: remove underscore character and capitalize the next character.

Input:

   word_example_one other_words ...   
   word_example_two other_words ...   
   word_example_three other_words ...  

Expected output:

   wordExampleOne other_words ...  
   wordExampleTwo other_words ...  
   wordExampleThree other_words ...  

Answer 1

You could try substitute with :h sub-replace-special:

:%s/^\w\+/\=substitute(submatch(0), '_\(\a\)', '\u\1', 'g')

with :%s/^\w\+/ you target first word, then with special replace, you substitute within whole match (first word in our case), using :h substitute() function.

Thus, having text like:

word_example_one ...  word_example_one ...
word_example_two ...  word_example_two ...
word_example_three ...  word_example_three ...

and running this command, you get:

wordExampleOne ...  word_example_one ...
wordExampleTwo ...  word_example_two ...
wordExampleThree ...  word_example_three ...

Answer 2

Another :substitute-based option, where the pattern is simpler:

:substitute/\v_(\a)/\u\1

and then use & to repeat this on the line until you are satisfied (it only changes the first _ in the line each time). If you want to repeat this across the whole file, use :%substitute first and then type g& as many times as necessary.

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With tpope's vim-abolish, crc coerces to camelCase. So you could do (for example)

:[range]normal ^crc

to change the first word on the lines covered by [range] to camel case.