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.\" Copyright (c) 2012 Jeremie Le Hen <jlh@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code and documentation must retain the above
.\" copyright notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd April 28, 2012
.Dt LIBSTDBUF 3
.Os
.Sh NAME
.Nm libstdbuf
.Nd preloaded library to change standard streams initial buffering
.Sh DESCRIPTION
The
.Nm
library is meant to be preloaded with the
.Ev LD_PRELOAD
environment variable to as to change the initial buffering
of standard input, standard output and standard error streams.
.Pp
Although you may load and configure this library manually,
an utility,
.Xr stdbuf 1 ,
can be used to run a command with the appropriate environment variables.
.Sh ENVIRONMENT
Each stream can be configured independently through the following
environment variables (values are defined below):
.Bl -tag -width size -offset indent
.It Ev _STDBUF_I
Initial buffering definition for the standard input stream
.It Ev _STDBUF_O
Initial buffering definition for the standard output stream
.It Ev _STDBUF_E
Initial buffering definition for the standard error stream
.El
.Pp
Each variable may take one of the following values:
.Bl -tag -width size -offset indent
.It Qq 0
unbuffered
.It Qq L
line buffered
.It Qq B
fully buffered with the default buffer size
.It Ar size
fully buffered with a buffer of
.Ar size
bytes (suffixes 'k', 'M' and 'G' are accepted)
.El
.Sh EXAMPLE
In the following example, the stdout stream of the
.Xr awk 1
command
will be fully buffered by default because it does not refer
to a terminal.
.Nm
is used to force it to be line-buffered so
.Xr vmstat 8 Ns 's
output will not stall until the full buffer fills.
.Bd -literal -offset indent
# vmstat 1 | LD_PRELOAD=/usr/lib/libstdbuf.so \\
STDBUF_1=L awk '$2 > 1 || $3 > 1' | cat -n
.Ed
.Pp
See also the manpage of
.Xr stdbuf 1
for a simpler way to do this.
.Sh HISTORY
The
.Nm
library first appeared in
.Fx 8.4 .
.Sh AUTHORS
.An -nosplit
The original idea of the
.Nm
command comes from
.An Padraig Brady
who implemented it in the GNU coreutils.
.An Jeremie Le Hen
implemented it on
.Fx .
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