How to replace one character inside parentheses keep everything else as is

Question

The data looks like this :

There is stuff here (word, word number phrases)
(word number anything, word phrases), even more
...

There is a l

Answer 1

Assuming there's only one comma to be replaced inside parentheses, this POSIX BRE sed expression will replace it with colon:

sed 's/(\(.*\),\(.*\))/(\1:\2)/g' file

If there are more than one comma, only the last one will be replaced.

In multiple-commas scenario, you can replace only the first one with:

sed 's/(\([^,]*\),\([^)]*\))/(\1:\2)/g' file