xref: /freebsd/usr.bin/look/look.1 (revision 7df526eb10c9095e4988e77900f60ba00c42b095)

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.Dd December 29, 2020
.Dt LOOK 1
.Os
.Sh NAME
.Nm look
.Nd display lines beginning with a given string
.Sh SYNOPSIS
.Nm
.Op Fl df
.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.
As
.Nm
performs a binary search, the lines in
.Ar file
must be sorted.
.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 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 EXAMPLES
Look for lines starting with
.Ql xylen
in the file
.Pa /usr/share/dict/words :
.Bd -literal -offset indent
$ look xylen
xylene
xylenol
xylenyl
.Ed
.Pp
Same as above, but do not consider any characters in
.Ar string
beyond the first
.Ql e .
Note that
.Fl f
is implicit since we are searching the default file
.Pa /usr/share/dict/words :
.Bd -literal -offset indent
$ look -t e xylen
Xyleborus
xylem
xylene
xylenol
xylenyl
xyletic
.Ed
.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
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 .