Searches for a pattern in files
grep [options] pattern [file-list]
The grep utility searches one or more files, line by line, for a pattern, which can be a simple string or another form of a regular expression. The grep utility takes various actions, specified by options, each time it finds a line that contains a match for the pattern. The grep utility takes its input from files you specify on the command line or from standard input.
The pattern is a regular expression, as defined in Appendix A. You must quote regular expressions that contain special characters, SPACEs, or TABs. An easy way to quote these characters is to enclose the entire expression within single quotation marks.
The file-list contains pathnames of ordinary ...