/usr.bin/tail/tail.1
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- .\" @(#)tail.1 8.1 (Berkeley) 6/6/93
- .\" $FreeBSD$
- .\"
- .Dd June 5, 2009
- .Dt TAIL 1
- .Os
- .Sh NAME
- .Nm tail
- .Nd display the last part of a file
- .Sh SYNOPSIS
- .Nm
- .Op Fl F | f | r
- .Op Fl q
- .Oo
- .Fl b Ar number | Fl c Ar number | Fl n Ar number
- .Oc
- .Op Ar
- .Sh DESCRIPTION
- The
- .Nm
- utility displays the contents of
- .Ar file
- or, by default, its standard input, to the standard output.
- .Pp
- The display begins at a byte, line or 512-byte block location in the
- input.
- Numbers having a leading plus
- .Pq Ql +
- sign are relative to the beginning
- of the input, for example,
- .Dq Li "-c +2"
- starts the display at the second
- byte of the input.
- Numbers having a leading minus
- .Pq Ql -
- sign or no explicit sign are
- relative to the end of the input, for example,
- .Dq Li "-n 2"
- displays the last two lines of the input.
- The default starting location is
- .Dq Li "-n 10" ,
- or the last 10 lines of the input.
- .Pp
- The options are as follows:
- .Bl -tag -width indent
- .It Fl b Ar number
- The location is
- .Ar number
- 512-byte blocks.
- .It Fl c Ar number
- The location is
- .Ar number
- bytes.
- .It Fl f
- The
- .Fl f
- option causes
- .Nm
- to not stop when end of file is reached, but rather to wait for additional
- data to be appended to the input.
- The
- .Fl f
- option is ignored if the standard input is a pipe, but not if it is a FIFO.
- .It Fl F
- The
- .Fl F
- option implies the
- .Fl f
- option, but
- .Nm
- will also check to see if the file being followed has been renamed or rotated.
- The file is closed and reopened when
- .Nm
- detects that the filename being read from has a new inode number.
- .Pp
- If the file being followed does not (yet) exist or if it is removed, tail
- will keep looking and will display the file from the beginning if and when
- it is created.
- .Pp
- The
- .Fl F
- option is the same as the
- .Fl f
- option if reading from standard input rather than a file.
- .It Fl n Ar number
- The location is
- .Ar number
- lines.
- .It Fl q
- Suppresses printing of headers when multiple files are being examined.
- .It Fl r
- The
- .Fl r
- option causes the input to be displayed in reverse order, by line.
- Additionally, this option changes the meaning of the
- .Fl b , c
- and
- .Fl n
- options.
- When the
- .Fl r
- option is specified, these options specify the number of bytes, lines
- or 512-byte blocks to display, instead of the bytes, lines or blocks
- from the beginning or end of the input from which to begin the display.
- The default for the
- .Fl r
- option is to display all of the input.
- .El
- .Pp
- If more than a single file is specified, each file is preceded by a
- header consisting of the string
- .Dq Li "==> " Ns Ar XXX Ns Li " <=="
- where
- .Ar XXX
- is the name of the file unless
- .Fl q
- flag is specified.
- .Sh EXIT STATUS
- .Ex -std
- .Sh SEE ALSO
- .Xr cat 1 ,
- .Xr head 1 ,
- .Xr sed 1
- .Sh STANDARDS
- The
- .Nm
- utility is expected to be a superset of the
- .St -p1003.2-92
- specification.
- In particular, the
- .Fl F ,
- .Fl b
- and
- .Fl r
- options are extensions to that standard.
- .Pp
- The historic command line syntax of
- .Nm
- is supported by this implementation.
- The only difference between this implementation and historic versions
- of
- .Nm ,
- once the command line syntax translation has been done, is that the
- .Fl b ,
- .Fl c
- and
- .Fl n
- options modify the
- .Fl r
- option, i.e.,
- .Dq Li "-r -c 4"
- displays the last 4 characters of the last line
- of the input, while the historic tail (using the historic syntax
- .Dq Li -4cr )
- would ignore the
- .Fl c
- option and display the last 4 lines of the input.
- .Sh HISTORY
- A
- .Nm
- command appeared in PWB UNIX.