Linux Commands Examples

A great documentation place for Linux commands


display lines beginning with a given string

see also : grep - sort


look [-bdf] [-t termchar] string [file ...]

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The look utility displays any lines in file which contain string as a prefix.

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.

The following options are available:


Use a binary search on the given word list. If you are ignoring case with -f or ignoring non-alphanumeric characters with -d, the file must be sorted in the same way. Please note that these options are the default if no filename is given. See sort(1) for more information on sorting files.


Dictionary character set and order, i.e., only alphanumeric characters are compared.


Ignore the case of alphabetic characters.


Specify a string termination character, i.e., only the characters in string up to and including the first occurrence of termchar are compared.


The original manual page stated that tabs and blank characters participated in comparisons when the -d option was specified. This was incorrect and the current man page matches the historic implementation.

look uses a linear search by default instead of a binary search, which is what most other implementations use by default.


The LANG, LC_ALL and LC_CTYPE environment variables affect the execution of the look utility. Their effect is described in environ(7).

exit status


the dictionary

The look utility exits 0 if one or more lines were found and displayed, 1 if no lines were found, and >1 if an error occurred.


Lines are not compared according to the current locale’s collating order. Input files must be sorted with LC_COLLATE set to ’C’.

BSD July 17, 2004 BSD


A look utility appeared in Version 7 AT&T UNIX.

see also

grep , sort

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