/usr.bin/tail/tail.1

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 31.\"	@(#)tail.1	8.1 (Berkeley) 6/6/93
 32.\" $FreeBSD$
 33.\"
 34.Dd June 5, 2009
 35.Dt TAIL 1
 36.Os
 37.Sh NAME
 38.Nm tail
 39.Nd display the last part of a file
 40.Sh SYNOPSIS
 41.Nm
 42.Op Fl F | f | r
 43.Op Fl q
 44.Oo
 45.Fl b Ar number | Fl c Ar number | Fl n Ar number
 46.Oc
 47.Op Ar
 48.Sh DESCRIPTION
 49The
 50.Nm
 51utility displays the contents of
 52.Ar file
 53or, by default, its standard input, to the standard output.
 54.Pp
 55The display begins at a byte, line or 512-byte block location in the
 56input.
 57Numbers having a leading plus
 58.Pq Ql +
 59sign are relative to the beginning
 60of the input, for example,
 61.Dq Li "-c +2"
 62starts the display at the second
 63byte of the input.
 64Numbers having a leading minus
 65.Pq Ql -
 66sign or no explicit sign are
 67relative to the end of the input, for example,
 68.Dq Li "-n 2"
 69displays the last two lines of the input.
 70The default starting location is
 71.Dq Li "-n 10" ,
 72or the last 10 lines of the input.
 73.Pp
 74The options are as follows:
 75.Bl -tag -width indent
 76.It Fl b Ar number
 77The location is
 78.Ar number
 79512-byte blocks.
 80.It Fl c Ar number
 81The location is
 82.Ar number
 83bytes.
 84.It Fl f
 85The
 86.Fl f
 87option causes
 88.Nm
 89to not stop when end of file is reached, but rather to wait for additional
 90data to be appended to the input.
 91The
 92.Fl f
 93option is ignored if the standard input is a pipe, but not if it is a FIFO.
 94.It Fl F
 95The
 96.Fl F
 97option implies the
 98.Fl f
 99option, but
100.Nm
101will also check to see if the file being followed has been renamed or rotated.
102The file is closed and reopened when
103.Nm
104detects that the filename being read from has a new inode number.
105.Pp
106If the file being followed does not (yet) exist or if it is removed, tail
107will keep looking and will display the file from the beginning if and when
108it is created.
109.Pp
110The
111.Fl F
112option is the same as the
113.Fl f
114option if reading from standard input rather than a file.
115.It Fl n Ar number
116The location is
117.Ar number
118lines.
119.It Fl q
120Suppresses printing of headers when multiple files are being examined.
121.It Fl r
122The
123.Fl r
124option causes the input to be displayed in reverse order, by line.
125Additionally, this option changes the meaning of the
126.Fl b , c
127and
128.Fl n
129options.
130When the
131.Fl r
132option is specified, these options specify the number of bytes, lines
133or 512-byte blocks to display, instead of the bytes, lines or blocks
134from the beginning or end of the input from which to begin the display.
135The default for the
136.Fl r
137option is to display all of the input.
138.El
139.Pp
140If more than a single file is specified, each file is preceded by a
141header consisting of the string
142.Dq Li "==> " Ns Ar XXX Ns Li " <=="
143where
144.Ar XXX
145is the name of the file unless
146.Fl q
147flag is specified.
148.Sh EXIT STATUS
149.Ex -std
150.Sh SEE ALSO
151.Xr cat 1 ,
152.Xr head 1 ,
153.Xr sed 1
154.Sh STANDARDS
155The
156.Nm
157utility is expected to be a superset of the
158.St -p1003.2-92
159specification.
160In particular, the
161.Fl F ,
162.Fl b
163and
164.Fl r
165options are extensions to that standard.
166.Pp
167The historic command line syntax of
168.Nm
169is supported by this implementation.
170The only difference between this implementation and historic versions
171of
172.Nm ,
173once the command line syntax translation has been done, is that the
174.Fl b ,
175.Fl c
176and
177.Fl n
178options modify the
179.Fl r
180option, i.e.,
181.Dq Li "-r -c 4"
182displays the last 4 characters of the last line
183of the input, while the historic tail (using the historic syntax
184.Dq Li -4cr )
185would ignore the
186.Fl c
187option and display the last 4 lines of the input.
188.Sh HISTORY
189A
190.Nm
191command appeared in PWB UNIX.