popen(3)popen(3)NAMEpopen - Initiates a pipe to a process
SYNOPSIS
#include <stdio.h>
FILE *popen(
const char *command,
const char *type );
LIBRARY
Standard C Library (libc)
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
popen(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Points to a null-terminated string containing a shell command line.
Points to a null-terminated string containing an I/O mode.
DESCRIPTION
The popen() function creates a pipe between the calling program and a
shell command to be executed. It returns a pointer to a FILE structure
for the stream.
If the type parameter is the value r, the calling program can read from
the standard output of the command by reading from the returned file
stream. If the type parameter is the value w, the calling program can
write to the standard input of the command by writing to the returned
file stream.
Because open files are shared, a type r command can be used as an input
filter and a type w command as an output filter.
NOTES
Programs using the popen() function to invoke an output filter should
beware of possible deadlock caused by output data remaining in the pro‐
gram's buffer. This can be avoided by either using the setbuf() func‐
tion to ensure that the output stream is unbuffered, or by using the
fflush() function to ensure that all buffered data is flushed before
calling the pclose() function.
Caution
If the original processes and the process started with the popen()
function concurrently read or write a common file, neither should use
buffered I/O. If they do, the results are unpredictable.
RETURN VALUES
Upon successful completion, the popen() function returns a pointer to
the FILE structure for the opened stream. In case of error because
files or processes could not be created, the popen() function returns a
null pointer.
SEE ALSO
Functions: exec(2), fork(2), fclose(3), fopen(3), pclose(3), pipe(2),
setbuf(3)
Standards: standards(5)popen(3)