Awk or grep question

Question

I have this datafile

[abc]
def
ghi
[jkl]
[mno]

From this file; i can run grep and easily get all lines that have "[" in them. How can I get the contents of text inside "[]".

For example:

abc
jkl
mno

Thanks

Answer 1

Give this a try:

sed -n 's/\[\([^]]*\)\]/\1/p'

or

awk -F "[][]" '$2 != "" {print $2}'

or

grep -Po '(?<=\[)[^]]*(?=])'