popen - Initiates a pipe to a process
const char *command,
const char *type );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
popen(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Points to a null-terminated string containing a shell command
line. Points to a null-terminated string containing
an I/O mode.
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
Because open files are shared, a type r command can be
used as an input filter and a type w command as an output
Programs using the popen() function to invoke an output
filter should beware of possible deadlock caused by output
data remaining in the program's buffer. This can be
avoided by either using the setbuf() function 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.
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
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.
Functions: exec(2), fork(2), fclose(3), fopen(3),
pclose(3), pipe(2), setbuf(3)
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