问题
I would like to match these characters: [ ] ( ) in a character class in a regex, how can I do that?
echo 'some text (some text in parenthesis) [some other in brackets]' | grep '[\[\]\(\)]'
This one doesn't match any character.
回答1:
You can use it like this:
echo 'some text (some text in paranthesis) [some other in brackets]' | grep -o '[][()]'
(
)
[
]
You don't need to escape ( and ) inside a character class. Moreover if you place ] and [ right after opening [ then you don't need to escape them either.
回答2:
Just FYI:
Accoding to the grep documentation, section 3.2 Character Classes and Bracket Expressions:
Most meta-characters lose their special meaning inside bracket expressions.
‘]’
ends the bracket expression if it’s not the first list item. So, if you want to make the ‘]’ character a list item, you must put it first.
Also, you can see that (, [ and ) are not special in the bracket expressions.
Since ] in your '[\[\]\(\)]' bracket expression pattern is not the first character, it ends the pattern, and the next ] created an incomplete bracket expression.
回答3:
The most common way is to put a \ before the character, but oddly enough that doesn't seem to work for ] with grep.
If you can use Perl, do this:
% cat yourfile.txt | perl -ne 'print if(/[\[\]\(\)]/);';
来源：https://stackoverflow.com/questions/37091691/regex-brackets-and-parenthesis-in-character-class