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LOOK(1) User Commands LOOK(1)


look - display lines beginning with a given string


look [options] string [file]


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(1) was given 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.


-a, --alternative

Use the alternative dictionary file.

-d, --alphanum

Use normal dictionary character set and order, i.e., only blanks and alphanumeric characters are compared. This is on by default if no file is specified.

Note that blanks have been added to dictionary character set for compatibility with sort -d command since version 2.28.

-f, --ignore-case

Ignore the case of alphabetic characters. This is on by default if no file is specified.

-t, --terminate character

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

-h, --help

Display help text and exit.

-V, --version

Print version and exit.

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.



Path to a dictionary file. The environment variable has greater priority than the dictionary path defined in the FILES segment.



the dictionary


the alternative dictionary


The look utility appeared in Version 7 AT&T Unix.


sort -d /etc/passwd -o /tmp/look.dict
look -t: root:foobar /tmp/look.dict


grep(1), sort(1)


For bug reports, use the issue tracker at <>.


The look command is part of the util-linux package which can be downloaded from Linux Kernel Archive <>.

2022-05-11 util-linux 2.38.1