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35 .\" @(#)tail.1 8.1 (Berkeley) 6/6/93
36 .\" $FreeBSD: src/usr.bin/tail/tail.1,v 1.5.2.4 2002/07/15 07:46:27 keramida Exp $
37 .\" $DragonFly: src/usr.bin/tail/tail.1,v 1.3 2007/07/30 22:11:33 swildner Exp $
38 .\"
39 .Dd June 6, 1993
40 .Dt TAIL 1
41 .Os
42 .Sh NAME
43 .Nm tail
44 .Nd display the last part of a file
45 .Sh SYNOPSIS
46 .Nm
47 .Oo
48 .Fl F |
49 .Fl f |
50 .Fl r
51 .Oc
52 .Oo
53 .Fl b Ar number |
54 .Fl c Ar number |
55 .Fl n Ar number
56 .Oc
57 .Op Ar
58 .Sh DESCRIPTION
59 The
60 .Nm
61 utility displays the contents of
62 .Ar file
63 or, by default, its standard input, to the standard output.
64 .Pp
65 The display begins at a byte, line or 512-byte block location in the
66 input.
67 Numbers having a leading plus (``+'') sign are relative to the beginning
68 of the input, for example,
69 .Dq -c +2
70 starts the display at the second
71 byte of the input.
72 Numbers having a leading minus (``-'') sign or no explicit sign are
73 relative to the end of the input, for example,
74 .Dq -n 2
75 displays the last two lines of the input.
76 The default starting location is
77 .Dq -n 10 ,
78 or the last 10 lines of the input.
79 .Pp
80 The options are as follows:
81 .Bl -tag -width Ds
82 .It Fl b Ar number
83 The location is
84 .Ar number
85 512-byte blocks.
86 .It Fl c Ar number
87 The location is
88 .Ar number
89 bytes.
90 .It Fl f
91 The
92 .Fl f
93 option causes
94 .Nm
95 to not stop when end of file is reached, but rather to wait for additional
96 data to be appended to the input.
97 The
98 .Fl f
99 option is ignored if the standard input is a pipe, but not if it is a FIFO.
100 .It Fl F
101 The
102 .Fl F
103 option implies the
104 .Fl f
105 option, but
106 .Nm
107 will also check to see if the file being followed has been renamed or rotated.
108 The file is closed and reopened when
109 .Nm
110 detects that the filename being read from has a new inode number.
111 The
112 .Fl F
113 option is ignored if reading from standard input rather than a file.
114 .It Fl n Ar number
115 The location is
116 .Ar number
117 lines.
118 .It Fl r
119 The
120 .Fl r
121 option causes the input to be displayed in reverse order, by line.
122 Additionally, this option changes the meaning of the
123 .Fl b ,
124 .Fl c
125 and
126 .Fl n
127 options.
128 When the
129 .Fl r
130 option is specified, these options specify the number of bytes, lines
131 or 512-byte blocks to display, instead of the bytes, lines or blocks
132 from the beginning or end of the input from which to begin the display.
133 The default for the
134 .Fl r
135 option is to display all of the input.
136 .El
137 .Pp
138 If more than a single file is specified, each file is preceded by a
139 header consisting of the string
140 .Dq ==> XXX <==
141 where
142 .Dq XXX
143 is the name of the file.
144 .Sh DIAGNOSTICS
145 .Ex -std
146 .Sh SEE ALSO
147 .Xr cat 1 ,
148 .Xr head 1 ,
149 .Xr sed 1
150 .Sh STANDARDS
151 The
152 .Nm
153 utility is expected to be a superset of the
154 .St -p1003.2-92
155 specification.
156 In particular, the
157 .Fl F ,
158 .Fl b
159 and
160 .Fl r
161 options are extensions to that standard.
162 .Pp
163 The historic command line syntax of
164 .Nm
165 is supported by this implementation.
166 The only difference between this implementation and historic versions
167 of
168 .Nm ,
169 once the command line syntax translation has been done, is that the
170 .Fl b ,
171 .Fl c
172 and
173 .Fl n
174 options modify the
175 .Fl r
176 option, i.e. ``-r -c 4'' displays the last 4 characters of the last line
177 of the input, while the historic tail (using the historic syntax ``-4cr'')
178 would ignore the
179 .Fl c
180 option and display the last 4 lines of the input.
181 .Sh HISTORY
182 A
183 .Nm
184 command appeared in PWB
185 .Ux .