The name grep can be traced back to the ex editor. If you invoked that editor and wanted to search for a string, you would type at the ex prompt:
The first line containing the string pattern would be printed as "p" by the print command. If you wanted all the lines that contained pattern to be printed, you would type:
When g precedes pattern, it means "all lines in the file," or "perform a global substitution."
Because the search pattern is called a regular expression, we can substitute RE for pattern and the command reads:
And there you have it. The meaning of grep and the rigin of its name. It means "g lobally search for the regular expression (RE) and ...