grep 'word1\|word2\|word3' /path/to/file
### Search all text files ###
$ grep 'word*' *.txt
### Search all python files for 'wordA' or 'wordB' ###
$ grep 'wordA*'\''wordB' *.py
$ grep -E 'word1|word2' *.doc
$ grep -e string1 -e string2 *.pl
$ grep -E "word1|word2" *.c
### Show all the lines that do not match given pattern/words/strings ###
$ grep -v 'bar\|foo' /dir1/dir2/file1
$ grep -E -v 'pattern1|pattern2' /path/to/file