Using grep

A long time ago, as the idea of regular expressions was catching on, the line editor ed contained a command to display lines of a file being edited that matched a given regular expression. The command is:

g/regular expression/p

That is, “on a global basis, print the current line when a match for regular expression is found,” or more simply, “global regular expression print.” This function was so useful that it was made into a standalone utility named, appropriately, grep. Later, the regular expression grammar of grep was expanded in a new command called egrep (for “extended grep”). You’ll find both commands on your Linux system today, and they differ slightly in the way they handle regular expressions. For the purposes of Exam 101, we’ll stick with grep, which can also make use of the “extended” regular expressions when used with the -E option. You will find some form of grep on just about every Unix or Unix-like system available.

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