usr.bin/truncate/truncate.1

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.\" Copyright (c) 2000 Sheldon Hearn <sheldonh@FreeBSD.org>.
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.\" $FreeBSD: src/usr.bin/truncate/truncate.1,v 1.4.2.7 2001/08/16 13:17:08 ru Exp $
.\"
.Dd February 2, 2018
.Dt TRUNCATE 1
.Os
.Sh NAME
.Nm truncate
.Nd truncate or extend the length of files
.Sh SYNOPSIS
.Nm
.Op Fl c
.Bk -words
.Fl s Xo
.Sm off
.Op Cm + | -
.Ar size
.Op Cm K | M | G | T
.Sm on
.Xc
.Ek
.Ar
.Nm
.Op Fl c
.Bk -words
.Fl r Ar rfile
.Ek
.Ar
.Sh DESCRIPTION
The
.Nm
utility adjusts the length of each regular file given on the command-line.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl c
Do not create files if they do not exist.
The
.Nm
utility does not treat this as an error.
No error messages are displayed
and the exit value is not affected.
.It Fl r Ar rfile
Truncate files to the length of the file
.Ar rfile .
.It Fl s Xo
.Sm off
.Op Cm + | -
.Ar size
.Op Cm K | M | G | T
.Sm on
.Xc
If the
.Ar size
argument is preceded by a plus sign
.Pq Cm + ,
files will be extended by this number of bytes.
If the
.Ar size
argument is preceded by a dash
.Pq Cm - ,
file lengths will be reduced by no more than this number of bytes,
to a minimum length of zero bytes.
Otherwise, the
.Ar size
argument specifies an absolute length to which all files
should be extended or reduced as appropriate.
.Pp
The
.Ar size
argument may be suffixed with one of
.Cm K ,
.Cm M ,
.Cm G
or
.Cm T
to indicate a multiple of
Kilobytes, Megabytes, Gigabytes or Terabytes
respectively.
.El
.Pp
Exactly one of the
.Fl r
and
.Fl s
options must be specified.
.Pp
If a file is made smaller, its extra data is lost.
If a file is made larger,
it will be extended as if by writing bytes with the value zero.
If the file does not exist,
it is created unless the
.Fl c
option is specified.
.Pp
Note that,
while truncating a file causes space on disk to be freed,
extending a file does not cause space to be allocated.
To extend a file and actually allocate the space,
it is necessary to explicitly write data to it,
using (for example) the shell's
.Ql >>
redirection syntax, or
.Xr dd 1 .
.Sh EXIT STATUS
.Ex -std
.Sh DIAGNOSTICS
If the operation fails for an argument,
.Nm
will issue a diagnostic
and continue processing the remaining arguments.
.Sh SEE ALSO
.Xr dd 1 ,
.Xr touch 1 ,
.Xr truncate 2
.Sh STANDARDS
The
.Nm
utility conforms to no known standards.
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 4.2 .
.Sh AUTHORS
The
.Nm
utility was written by
.An Sheldon Hearn Aq Mt sheldonh@starjuice.net .