Grep value between strings with regex

Question

$ acpi

Battery 0: Charging, 18%, 01:37:09 until charged

How to grep the battery level value without percentage character (18)?

This should do it but I'm getting an empty result:

acpi | grep -e '(?<=, )(.*)(?=%)'

Answer 1

Your regex is correct but will work with experimental -P or perl mode regex option in gnu grep. You will also need -o to show only matching text.

Correct command would be:

grep -oP '(?<=, )\d+(?=%)'

However, if you don't have gnu grep then you can also use sed like this:

sed -nE 's/.*, ([0-9]+)%.*/\1/p' file

18