Replace a character multiple times but within pattern

Question

I am creating a yml file out of some variables. I have like 80 lines and they all have the pattern:

my-first-command-line-var: {{ my-first-command-line-var }},
my-second-cli-var: {{ {{ my-second-cli-var }} ,
my-third-var: {{ my-third-var }}

and so on

That's because all cli variables are with - but yaml can't handle _.

So I need to replace all - inside {{ }} with a _, so it becomes:

my-first-command-line-var: {{ my_first_command_line_var }},
my-second-cli-var: {{ {{ my_second_cli_var }} ,
my-third-var: {{ my_third_var }}

I have tried :%s/{{\zs\-*ze}}/_/g and some variations like :%s/{{\zs\(-\)*ze}}/_/g but nothing like this worked.

Answer 1

You can use a :s command with an expression on the replacement side (see :help sub-replace-expression), then you can use the substitute() function to perform the replacement of - for _, and the submatch() function to refer to the match.

For your specific case, the following command will work:

:%s/{{.*}}/\=substitute(submatch(0), "-", "_", "g")

This will match the contents in between {{ and }} on every line. And it will replace it with the result of the function call, which takes the matched contents (as submatch(0)) and replaces all -s with _s.