Grep command

From RZWiki

A command line program available on Linux platforms; used to used to search for regular expressions within files.

Usage Syntax

grep [options] string [file/file_pattern...]

Common options include;

-r or -R - read files recursively
-A nn - display the specified nn number of lines after each match
-B nn - display the specified nn number of lines before each match
-C nn - context: display the specified nn number of lines before and after each match
-c - count: display a count of lines containing the specified string
--colour - colour the matching string in any output
-E - interpret the specified string as an extended regular expression
-f - obtain search strings from the specified file
-H - prefix each line of output with the file name the match was found in
-i - ignore case in both the specified string and file
-n - prefix each line of output with the line number of the match in the file

Usage Examples

grep -R -C 5 power.png * - search for the string power.png in all files (*) in the present working directory and any subdirectories (-R) and display 5 lines of text before and after each match (-C 5)

Usage Notes

string can include regular expressions

Linux Usage Notes

With most Linux or Unix commands;

Non root users may need to prefix commands with the sudo command, for example: sudo chmod 644 *
Brief help can be displayed using the -h or --help parameter, for example: chmod --help
A full command manual can be displayed using the man command followed by the command name, for example: man chmod
Sometimes 'info' pages are used instead of or to provide more information than man pages; for example: info chmod
Version information can normally be display using the -v, -V or --version parameter, for example: chmod --version. However, this paramater is also frequently used to display verbose output.