look man page
look — display lines beginning with a given string
look [options] string [file]
The look utility displays any lines in file which contain string. 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.
- -V, --version
Display version information and exit.
- -h, --help
Display help text 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.
sort -d /etc/passwd -o /tmp/look.dict look -t: root:foobar /tmp/look.dict
the alternative dictionary
The look utility appeared in Version 7 AT&T Unix.
The look command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.