Note that these defaults maybe be altered using the

.Xr stdbuf 1

utility.

.Xr stdbuf 1 ,

.include <bsd.own.mk>

LIB= stdbuf

SRCS= stdbuf.c

SHLIB_MAJOR= 1

MAN= libstdbuf.3

WARNS?= 6

.include <bsd.lib.mk>

.Dd April 28, 2012

.Os

.Nm libstdbuf

.Nd preloaded library to change standard streams initial buffering

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.

Each stream can be configured indepentently 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

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.

The

.Nm

library first appeared in

.Fx 8.4 .

.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 .

#include <err.h>

#include <errno.h>

#include <limits.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

static const char *

stream_name(FILE *s)

{

if (s == stdin)

return "stdin";

if (s == stdout)

return "stdout";

if (s == stderr)

return "stderr";

/* This should not happen. */

abort();

}

static void

change_buf(FILE *s, const char *bufmode)

{

char *unit;

size_t bufsize;

int mode;

bufsize = 0;

if (bufmode[0] == '0' && bufmode[1] == '\0')

mode = _IONBF;

else if (bufmode[0] == 'L' && bufmode[1] == '\0')

mode = _IOLBF;

else if (bufmode[0] == 'B' && bufmode[1] == '\0') {

mode = _IOFBF;

bufsize = 0;

} else {

/*

errno = 0;

bufsize = strtol(bufmode, &unit, 0);

if (errno == EINVAL || errno == ERANGE || unit == bufmode)

warn("Wrong buffer mode '%s' for %s", bufmode,

stream_name(s));

switch (*unit) {

case 'G':

bufsize *= 1024 * 1024 * 1024;

break;

case 'M':

bufsize *= 1024 * 1024;

break;

case 'k':

bufsize *= 1024;

break;

case '\0':

break;

default:

warnx("Unknown suffix '%c' for %s", *unit,

stream_name(s));

return;

}

mode = _IOFBF;

}

if (setvbuf(s, NULL, mode, bufsize) != 0)

warn("Cannot set buffer mode '%s' for %s", bufmode,

stream_name(s));

}

__attribute__ ((constructor)) static void

stdbuf(void)

{

char *i_mode, *o_mode, *e_mode;

i_mode = getenv("_STDBUF_I");

o_mode = getenv("_STDBUF_O");

e_mode = getenv("_STDBUF_E");

if (e_mode != NULL)

change_buf(stderr, e_mode);

if (i_mode != NULL)

change_buf(stdin, i_mode);

if (o_mode != NULL)

change_buf(stdout, o_mode);

}

stdbuf \

PROG= stdbuf

SRCS= stdbuf.c

WARNS?= 6

.include <bsd.prog.mk>

.Dd April 28, 2012

.Os

.Nm stdbuf

.Nd change standard streams initial buffering

.Nm

.Op Fl e Ar bufdef

.Op Fl i Ar bufdef

.Op Fl o Ar bufdef

.Op Ar command Op ...

.Nm

is used to change the initial buffering of standard input,

standard output and/or standard error streams for

.Ar command .

It relies on

.Xr libstdbuf 3

which is loaded and configured by

.Nm

through environment variables.

.Pp

The options are as follows:

.Bl -tag -width Ds

.It Fl e Ar bufdef

Set initial buffering of the standard error stream for

.Ar command

as defined by

.Ar bufdef

.Pq see Sx BUFFER DEFINITION .

.It Fl i Ar bufdef

Set initial buffering of the standard input stream for

.Ar command

as defined by

.Ar bufdef

.Pq see Sx BUFFER DEFINITION .

.It Fl o Ar bufdef

Set initial buffering of the standard output stream for

.Ar command

as defined by

.Ar bufdef

.Pq see Sx BUFFER DEFINITION .

.El

Buffer definition is the same as in

.Xr libstdbuf 3 :

.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

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 | stdbuf -o L awk '$2 > 1 || $3 > 1' | cat -n

.Ed

.Xr libstdbuf 3 ,

.Xr setvbuf 3

The

.Nm

utility first appeared in

.Fx 8.4 .

.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 .