Grep not as a regular expression

Use fgrep (deprecated), grep -F or grep --fixed-strings, to make it treat the pattern as a list of fixed strings, instead of a regex.

For reference, the documentation mentions (excerpts):

-F --fixed-strings Interpret the pattern as a list of fixed
strings (instead of regular expressions), separated by newlines, any
of which is to be matched. (-F is specified by POSIX.)

fgrep is the same as grep -F. Direct invocation as fgrep is
deprecated, but is provided to allow historical applications that rely
on them to run unmodified.

For the complete reference, check:
https://www.gnu.org/savannah-checkouts/gnu/grep/manual/grep.html