Finding patterns in files using your buddy grep

Use grep <pattern> <filenames>. The grep command displays lines in the files matching <pattern> as well as the name of the file from which the matching lines come from. The command grep has many useful command line options. Please see its man page for more information. Here we will show some typical usage of grep.

The option -n makes grep display the line number in front of the line that contains the given pattern. For example:

[amit@dslamit amit]$ grep color .bashrc
alias ls='ls --color=auto'
        [ -f /etc/profile.d/color_ls.sh ] && source /etc/profile.d/color_ls.sh
# setup for color ls
[amit@dslamit amit]$ grep -n color .bashrc
14:alias ls='ls --color=auto'
23:     [ -f /etc/profile.d/color_ls.sh ] && source /etc/profile.d/color_ls.sh
60:# setup for color ls
[amit@dslamit amit]$

The option -v inverts the search by finding lines that do not match the pattern.

The option -i asks grep to ignore case in the search string.

A very powerful option is the recursive search option, -r, that will make grep search recursively in a directory or directories. For example, the following command searches for all files with the string ``Crow'' in them.

[amit@onyx examples]: grep -r "Crow" C-examples/
C-examples/plugins/plugin1.c:/* Author: Dan Crow
C-examples/plugins/plugin2.c:/* Author: Dan Crow
C-examples/plugins/runplug.c:/* Author: Dan Crow (modified by Amit Jain)
[amit@onyx examples]:

Programmers often use this option to quickly search for a declaration of a structure in a large project consisting of hundreds or thousands of files in many directories and subdirectories. This is often called ``grepping'' the source! See the following for an example.

[amit@onyx examples]: grep -rn "struct list {" C-examples/
C-examples/files/checkpoint/List.h:17:struct list {
C-examples/doublyLinkedLists.private/library/List.h:17:struct list {
C-examples/include/List.h:17:struct list {
C-examples/doublyLinkedLists/List.h:17:struct list {
C-examples/doublyLinkedLists/bad/List.h:17:struct list {
C-examples/doublyLinkedLists/library/List.h:17:struct list {
[amit@onyx examples]: