grep -Eo -m 1 including extra characters after first match ; (treating a bracketed characters as a single pattern)

Question

I found this answer: Group matching with grep includes extra characters but the anwser doesn't work for me.

I have a line in a json file that looks like this:

"object.0.1_foo": {  

I want to match only the : in this case, other times I want to match the {.

grep -Eo -m 1 '[\:\{\}\[\]' <<<$object

returns : {

It was my understanding that characters inside brackets are the only thing searched for and if I ask for only the first match I should get just :

It seems like grep is treating \:\{ as a single 'character'. What's really odd to me is if I use this regex:

grep -Eo -m 1 '[^\s][\:\{\}\[\]' <<<$object

to exclude the space trying to force grep to see : and { as two distinct characters it returns

":

which is really confusing to me because the " is not in my regex at all.

I can't figure out how to adjust my regex to only get the single match.

Answer 1

-m 1 says to stop after 1 matching line; since there are two matching characters, -o will print them both (although it should be on two separate lines).

In addition, characters are literal inside [..] so [^\s] is matching any single character that is not \ or s. In your case, that is the leading ".

If you really want to return only the :, then all you need is grep -o ':'