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.\"     @(#)look.1	8.1 (Berkeley) 6/14/93
.\" $FreeBSD: head/usr.bin/look/look.1 314436 2017-02-28 23:42:47Z imp $
.\"
.Dd July 17, 2004
.Dt LOOK 1
.Os
.Sh NAME
.Nm look
.Nd display lines beginning with a given string
.Sh SYNOPSIS
.Nm
.Op Fl bdf
.Op Fl t Ar termchar
.Ar string
.Op Ar
.Sh DESCRIPTION
The
.Nm
utility displays any lines in
.Ar file
which contain
.Ar string
as a prefix.
.Pp
If
.Ar file
is not specified, the file
.Pa /usr/share/dict/words
is used, only alphanumeric characters are compared and the case of
alphabetic characters is ignored.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl b, -binary
Use a binary search on the given word list. If you are ignoring case with
.Fl f
or ignoring non-alphanumeric characters with
.Fl d ,
the file must be sorted in the same way. Please note that these options are the
default if no filename is given. See
.Xr sort 1
for more information on sorting files. 
.It Fl d , -alphanum
Dictionary character set and order, i.e., only alphanumeric characters
are compared.
.It Fl f , -ignore-case
Ignore the case of alphabetic characters.
.It Fl t , -terminate Ar termchar
Specify a string termination character, i.e., only the characters
in
.Ar string
up to and including the first occurrence of
.Ar termchar
are compared.
.El
.Sh ENVIRONMENT
The
.Ev LANG , LC_ALL
and
.Ev LC_CTYPE
environment variables affect the execution of the
.Nm
utility.
Their effect is described in
.Xr environ 7 .
.Sh FILES
.Bl -tag -width /usr/share/dict/words -compact
.It Pa /usr/share/dict/words
the dictionary
.El
.Sh EXIT STATUS
The
.Nm
utility exits 0 if one or more lines were found and displayed,
1 if no lines were found, and >1 if an error occurred.
.Sh COMPATIBILITY
The original manual page stated that tabs and blank characters participated
in comparisons when the
.Fl d
option was specified.
This was incorrect and the current man page matches the historic
implementation.
.Pp
.Nm
uses a linear search by default instead of a binary search, which is what most
other implementations use by default.
.Pp
The
.Fl a
and
.Fl -alternative
flags are ignored for compatibility.
.Sh SEE ALSO
.Xr grep 1 ,
.Xr sort 1
.Sh HISTORY
A
.Nm
utility appeared in
.At v7 .
.Sh BUGS
Lines are not compared according to the current locale's collating
order.
Input files must be sorted with
.Ev LC_COLLATE
set to
.Ql C .