How to search for whole words with grep?

Question

If I have the file foo:

read_from_buffer
read_from_buffer_and_file
write_to_buffer
some_other_function

then using

cat foo | grep 'read_from_buffer'

will list 2 lines:

read_from_buffer
read_from_buffer_and_file

But I want only exact matches... How to tell grep that different character must come than character: 0-9a-zA-Z_

Answer 1

Use this:

grep -w 'read_from_buffer' foo

---

From man grep:

-w, --word-regexp: Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character. Similarly, it must be either at the end of the line or followed by a non-word constituent character. Word-constituent characters are letters, digits, and the underscore.

or

-x, --line-regexp: Select only those matches that exactly match the whole line. (-x is specified by POSIX.)