On: Regular Expressions – Mastering Lookahead and Look...

[asicsp]

I often use `\K` instead, which also helps if it is variable length lookbehind

    $ echo 'foo=5, Bar=3; x1=83, y=120' | grep -oP '\b[a-z]+=\K\d+'
    5
    120

further reading: https://stackoverflow.com/questions/11640447/variable-length...