![]() Where the second line is the command given to ed to print the relevant lines, and the third line is the command to exit from the editor. Before grep existed as a separate command, the same effect might have been achieved in an editor: The name of grep derives from a usage in the Unix text editor ed and related programs. ![]() The following prints all lines in the file that begin with the letter a, followed by any one character, followed by the letter sequence ple. Regular expressions can be used to match more complicated text patterns. txt in a given directory may be searched if the shell supports globbing by using an asterisk as part of the filename: For example, all files having the extension. Multiple file names may be specified in the argument list. Case-insensitive matching occurs when the argument option -i (ignore case) is given. However, the search pattern specified as an argument is case sensitive by default, so this example's output does not include lines containing Apple (with a capital A) unless they also contain apple. Matches occur when the specific sequence of characters is recognized, for example, lines containing pineapple or apples are printed irrespective of word boundaries. By default, it reports matching lines on standard output, but specific modes of operation may be chosen with command line options.Ī simple example of a common usage of grep is the following, which searches the file fruitlist.txt for lines containing the text string apple: Grep searches files specified as arguments, or, if missing, the program's standard input. Grep's official creation date is given as March 3, 1973, in the Manual for Unix Version 4. In ed, the command g/re/p would print all lines matching a previously defined pattern. Grep was created by Ken Thompson as a standalone application adapted from the regular expression parser he had written for ed (which he also created).
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