How to find lines that contain ONLY lowercase using grep

Question

I am new to bash and am learning to use grep.

grep ^[a-z] file.txt will show all the lines that begin with lowercase
grep [a-z] file.txt all lines with lowercase

Can't figure out how to show lines with ALL lowercase, can anyone help?

Solution 1

You can use anchors in your regex for egrep:

egrep '^[[:lower:]]+$' file

This egrep will only find lines that have only lowercase letters in the (not even space is allowed).

Solution 2

This will match and exclude lines that contain something else besides a-z.

cat file.txt | grep -v '[^[:lower:]]'

If you need to allow symbols too (this example allows !, +, ,):

cat file.txt | grep -v '[^[:lower:]!+,]'