look Command in Linux with Examples

Description :

The look utility displays any lines in file which contain string as a prefix. As look performs a binary search, the lines in file must be sorted (where sort got the same options -d and/or -f that look is invoked with).
If file is not specified, the file /usr/share/dict/words is used, only alphanumeric characters are compared and the case of alphabetic characters is ignored.

Usage :

look [-dfab ] [-t termchar ] string [file ]

Options :

-b
Use binary search
-d
Dictionary character set and order, i.e. only alphanumeric characters are compared.
-f
Ignore the case of alphabetic characters.
-a
Use the alternate dictionary /usr/share/dict/web2
-t
Specify a string termination character, i.e. only the characters in string up to and including the first occurrence of termchar are compared.

Examples :

1. A Basic Example

Suppose you want to verify the spelling of the word rendezvous. You can do it easily using look command.

$ look rendez
rendezvous
rendezvous's
rendezvoused
rendezvouses
rendezvousing

2. Searching for a string in a file

For example, if I want to display all the header files that are included in a c file, I’d use the look command in the following way :

$ look "#include" test.c 
#include <stdio.h>
#include <stdlib.h>

3. Ignoring case while searching

When you want to know the spelling of a word which has the prefix ‘excl’.

$ look excl myfile
exclaimed
exclamation

This displays the word that starts with the given prefix (case sensitive) from file myfile.

$ look -f excl myfile
exclaimed
exclamation
EXCLAMATORY

4. Use Binary Search

$ look -bf excl myfile
exclaimed
exclamation
EXCLAMATORY