howto: Search for tab indent

grep -P '\t' config.yaml

In GNU Grep of some versions, searches for the string starting with a quotation mark, followed with "hello", followed with another quotation mark. Makes use of "-P", which turns on Perl regex. In Perl regex, "\x22" stands for a quotation mark, via standing for the character with the hexadecimal ASCII value of 22.

source: https://en.wikibooks.org/wiki/Grep