[unix-history] / usr / man / man3 / popen.3s

.TH POPEN 3S
.SH NAME
popen, pclose \- initiate I/O to/from a process
.SH SYNOPSIS
.B #include <stdio.h>
.PP
.SM
.B FILE
.B *popen(command, type)
.br
.B char *command, *type;
.PP
.B pclose(stream)
.br
.SM
.B FILE
.B *stream;
.SH DESCRIPTION
The arguments to 
.I popen
are pointers to null-terminated strings
containing respectively a shell command line and an I/O
mode, either "r" for reading or "w" for
writing.
It creates a pipe between
the calling process and
the command to be executed.
The value returned 
is a stream pointer that
can be used (as appropriate) to write to the standard input
of the command or read from its standard output.
.PP
A stream opened by
.I popen
should be closed by
.I pclose,
which waits for the associated process to terminate
and returns the exit status of the command.
.PP
Because open files are shared, a type "r" command
may be used as an input filter,
and a type "w" as an output filter.
.SH "SEE ALSO"
pipe(2),
fopen(3),
fclose(3),
system(3),
wait(2)
.SH DIAGNOSTICS
.I Popen
returns a null pointer
if files or processes cannot be created, or the Shell 
cannot be accessed.
.PP
.I Pclose
returns \-1 if
.I stream
is not associated with a `popened' command.
.SH BUGS
Buffered reading before opening an input filter
may leave the standard input of that filter mispositioned.
Similar problems with an output filter may be
forestalled by careful buffer flushing, e.g. with
.I fflush,
see
.IR fclose (3).
Commit	Line	Data
57e7635d TL	1	.TH POPEN 3S
	2	.SH NAME
	3	popen, pclose \- initiate I/O to/from a process
	4	.SH SYNOPSIS
	5	.B #include <stdio.h>
	6	.PP
	7	.SM
	8	.B FILE
	9	.B *popen(command, type)
	10	.br
	11	.B char command, type;
	12	.PP
	13	.B pclose(stream)
	14	.br
	15	.SM
	16	.B FILE
	17	.B *stream;
	18	.SH DESCRIPTION
	19	The arguments to
	20	.I popen
	21	are pointers to null-terminated strings
	22	containing respectively a shell command line and an I/O
	23	mode, either "r" for reading or "w" for
	24	writing.
	25	It creates a pipe between
	26	the calling process and
	27	the command to be executed.
	28	The value returned
	29	is a stream pointer that
	30	can be used (as appropriate) to write to the standard input
	31	of the command or read from its standard output.
	32	.PP
	33	A stream opened by
	34	.I popen
	35	should be closed by
	36	.I pclose,
	37	which waits for the associated process to terminate
	38	and returns the exit status of the command.
	39	.PP
	40	Because open files are shared, a type "r" command
	41	may be used as an input filter,
	42	and a type "w" as an output filter.
	43	.SH "SEE ALSO"
	44	pipe(2),
	45	fopen(3),
	46	fclose(3),
	47	system(3),
	48	wait(2)
	49	.SH DIAGNOSTICS
	50	.I Popen
	51	returns a null pointer
	52	if files or processes cannot be created, or the Shell
	53	cannot be accessed.
	54	.PP
	55	.I Pclose
	56	returns \-1 if
	57	.I stream
	58	is not associated with a `popened' command.
	59	.SH BUGS
	60	Buffered reading before opening an input filter
	61	may leave the standard input of that filter mispositioned.
	62	Similar problems with an output filter may be
	63	forestalled by careful buffer flushing, e.g. with
	64	.I fflush,
65	see
66	.IR fclose (3).