grep

grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command g/re/p (globally search for a regular expression and print matching lines), which has the same effect. grep was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9.

Document

GNU Grep 3.5

grep two pattens in the same line:

grep pattenA /var/log/log.txt | grep pattenA

search directories recursively:

grep -r pattenA /var/log/log.txt | grep pattenA