@node popen, unix
@subheading Syntax

@example
#include <stdio.h>

FILE *popen(const char *program, const char *mode);
@end example

@subheading Description

This function executes the named @code{program} and attaches either its
input stream or its output stream to the returned file.  While the file
is open, the calling program can write to the program (if the program
was open for writing) or read the program's output (if the program was
opened for reading).  When the program is done, or if you have no more
input for it, pass the file pointer to @code{pclose} (@pxref{pclose}),
which terminates the program. 

Since MS-DOS does not support multitasking, this function actually runs
the entire program when the program is opened for reading, and stores
the output in a temporary file.  @code{pclose} then removes that file. 
Similarly, when you open a program for writing, a temp file holds the
data and @code{pclose} runs the entire program.

The @var{mode} is the same as for @code{fopen} (@pxref{fopen}). 

@subheading Return Value

An open file which can be used to read the program's output or write to
the program's input. 

@subheading Portability

@portability !ansi, posix

@subheading Example

@example
FILE *p = popen("dir", "r");
read_program(p);
pclose(p);
@end example

@c ----------------------------------------------------------------------
@node pclose, unix
@subheading Syntax

@example
#include <stdio.h>

int pclose(FILE *pipe);
@end example

@subheading Description

This function closes a pipe opened with @code{popen} (@pxref{popen}). 
Note that since MS-DOS is not multitasking, this function will actually
run the program specified in @code{popen} if the pipe was opened for
writing. 

@subheading Return Value

Zero on success, nonzero on failure.

@subheading Portability

@portability !ansi, posix

@subheading Example

@example
FILE *f = popen("sort", "w");
write_to_pipe(f);
pclose(f);
@end example