2.3 Exit Status

Normally, the exit status is 0 if selected lines are found and 1 otherwise. But the exit status is 2 if an error occurred, unless the ‘-q’ or ‘--quiet’ or ‘--silent’ option is used and a selected line is found. Note, however, that POSIX only mandates, for programs such as grep, cmp, and diff, that the exit status in case of error be greater than 1; it is therefore advisable, for the sake of portability, to use logic that tests for this general condition instead of strict equality with 2.