xref: /freebsd/usr.bin/look/look.1 (revision f3f16c31fea258b2b1ec51ddd1bceb6207b66198)
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28.\"     @(#)look.1	8.1 (Berkeley) 6/14/93
29.\" $FreeBSD$
30.\"
31.Dd December 29, 2020
32.Dt LOOK 1
33.Os
34.Sh NAME
35.Nm look
36.Nd display lines beginning with a given string
37.Sh SYNOPSIS
38.Nm
39.Op Fl df
40.Op Fl t Ar termchar
41.Ar string
42.Op Ar
43.Sh DESCRIPTION
44The
45.Nm
46utility displays any lines in
47.Ar file
48which contain
49.Ar string
50as a prefix.
51As
52.Nm
53performs a binary search, the lines in
54.Ar file
55must be sorted.
56.Pp
57If
58.Ar file
59is not specified, the file
60.Pa /usr/share/dict/words
61is used, only alphanumeric characters are compared and the case of
62alphabetic characters is ignored.
63.Pp
64The following options are available:
65.Bl -tag -width indent
66.It Fl d , -alphanum
67Dictionary character set and order, i.e., only alphanumeric characters
68are compared.
69.It Fl f , -ignore-case
70Ignore the case of alphabetic characters.
71.It Fl t , -terminate Ar termchar
72Specify a string termination character, i.e., only the characters
73in
74.Ar string
75up to and including the first occurrence of
76.Ar termchar
77are compared.
78.El
79.Sh ENVIRONMENT
80The
81.Ev LANG , LC_ALL
82and
83.Ev LC_CTYPE
84environment variables affect the execution of the
85.Nm
86utility.
87Their effect is described in
88.Xr environ 7 .
89.Sh FILES
90.Bl -tag -width /usr/share/dict/words -compact
91.It Pa /usr/share/dict/words
92the dictionary
93.El
94.Sh EXIT STATUS
95The
96.Nm
97utility exits 0 if one or more lines were found and displayed,
981 if no lines were found, and >1 if an error occurred.
99.Sh EXAMPLES
100Look for lines starting with
101.Ql xylene
102in the file
103.Pa /usr/share/dict/words :
104.Bd -literal -offset indent
105$ look xylen
106xylene
107xylenol
108xylenyl
109.Ed
110.Pp
111Same as above, but do not consider any characters in
112.Ar string
113beyond the first
114.Ql e .
115Note that
116.Fl f
117is implicit since we are searching the default file
118.Pa /usr/share/dict/words :
119.Bd -literal -offset indent
120$ look -t e xylen
121Xyleborus
122xylem
123xylene
124xylenol
125xylenyl
126xyletic
127.Ed
128.Sh COMPATIBILITY
129The original manual page stated that tabs and blank characters participated
130in comparisons when the
131.Fl d
132option was specified.
133This was incorrect and the current man page matches the historic
134implementation.
135.Pp
136The
137.Fl a
138and
139.Fl -alternative
140flags are ignored for compatibility.
141.Sh SEE ALSO
142.Xr grep 1 ,
143.Xr sort 1
144.Sh HISTORY
145A
146.Nm
147utility appeared in
148.At v7 .
149.Sh BUGS
150Lines are not compared according to the current locale's collating
151order.
152Input files must be sorted with
153.Ev LC_COLLATE
154set to
155.Ql C .
156