look Man page

LOOK(1) BSD General Commands Manual LOOK(1)


look — display lines beginning with a given string


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


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

If file is not specified, the file /usr/share/dict/words is used, only
alphanumeric characters are compared and the case of alphabetic charac‐
ters is ignored.

The following options are available:

-b 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 for
more information on sorting files.

-d Dictionary character set and order, i.e., only alphanumeric char‐
acters are compared.

-f Ignore the case of alphabetic characters.

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

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

/usr/share/dict/words 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.

The original manual page stated that tabs and blank characters partici‐
pated in comparisons when the -d option was specified. This was incor‐
rect 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.


grep, sort

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


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