1.\" $NetBSD: tail.1,v 1.10 2001/12/08 19:17:23 wiz Exp $ 2.\" 3.\" Copyright (c) 1980, 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the Institute of Electrical and Electronics Engineers, Inc. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the University of 20.\" California, Berkeley and its contributors. 21.\" 4. Neither the name of the University nor the names of its contributors 22.\" may be used to endorse or promote products derived from this software 23.\" without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 26.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 27.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 28.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 29.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 30.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 31.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 32.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 34.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35.\" SUCH DAMAGE. 36.\" 37.\" @(#)tail.1 8.1 (Berkeley) 6/6/93 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 file ... 58.Sh DESCRIPTION 59The 60.Nm 61utility displays the contents of 62.Ar file 63or, by default, its standard input, to the standard output. 64.Pp 65The display begins at a byte, line or 512-byte block location in the 66input. 67Numbers having a leading plus (``+'') sign are relative to the beginning 68of the input, for example, 69.Dq -c +2 70starts the display at the second 71byte of the input. 72Numbers having a leading minus (``-'') sign or no explicit sign are 73relative to the end of the input, for example, 74.Dq -n 2 75displays the last two lines of the input. 76The default starting location is 77.Dq -n 10 , 78or the last 10 lines of the input. 79.Pp 80The options are as follows: 81.Bl -tag -width Ds 82.It Fl b Ar number 83The location is 84.Ar number 85512-byte blocks. 86.It Fl c Ar number 87The location is 88.Ar number 89bytes. 90.It Fl f 91The 92.Fl f 93option causes 94.Nm 95to not stop when end of file is reached, but rather to wait for additional 96data to be appended to the input. 97The 98.Fl f 99option is ignored if the standard input is a pipe, but not if it is a FIFO. 100.It Fl F 101The 102.Fl F 103option is the same as the 104.Fl f 105option, except that every five seconds 106.Nm 107will check to see if the file named on the command line has been 108shortened or moved (it is considered moved if the inode or device 109number changes) and, if so, it will close 110the current file, open the filename given, print out the entire 111contents, and continue to wait for more data to be appended. 112This option is used to follow log files though rotation by 113.Xr newsyslog 8 114or similar programs. 115.It Fl n Ar number 116The location is 117.Ar number 118lines. 119.It Fl r 120The 121.Fl r 122option causes the input to be displayed in reverse order, by line. 123Additionally, this option changes the meaning of the 124.Fl b , 125.Fl c 126and 127.Fl n 128options. 129When the 130.Fl r 131option is specified, these options specify the number of bytes, lines 132or 512-byte blocks to display, instead of the bytes, lines or blocks 133from the beginning or end of the input from which to begin the display. 134The default for the 135.Fl r 136option is to display all of the input. 137.El 138.Pp 139If more than a single file is specified, each file is preceded by a 140header consisting of the string 141.Dq ==> XXX <== 142where 143.Dq XXX 144is the name of the file. 145.Pp 146The 147.Nm 148utility exits 0 on success, and >0 if an error occurs. 149.Sh SEE ALSO 150.Xr cat 1 , 151.Xr head 1 , 152.Xr sed 1 153.Sh STANDARDS 154The 155.Nm 156utility is expected to be a superset of the 157.St -p1003.2-92 158specification. 159In particular, the 160.Fl b , 161.Fl r 162and 163.Fl F 164options are extensions to that standard. 165.Pp 166The historic command line syntax of 167.Nm 168is supported by this implementation. 169The only difference between this implementation and historic versions 170of 171.Nm "" , 172once the command line syntax translation has been done, is that the 173.Fl b , 174.Fl c 175and 176.Fl n 177options modify the 178.Fl r 179option, i.e. ``-r -c 4'' displays the last 4 characters of the last line 180of the input, while the historic tail (using the historic syntax ``-4cr'') 181would ignore the 182.Fl c 183option and display the last 4 lines of the input. 184.Sh HISTORY 185A 186.Nm 187command appeared in 188.At v7 . 189.Sh BUGS 190When using the 191.Fl F 192option, 193.Nm 194will not detect a file truncation if, between the truncation 195and the next check of the file size, data written to the file make 196it larger than the last known file size. 197