POPEN(3) Library Functions Manual POPEN(3)
popen, pclose - initiate I/O to/from a process
FILE *popen(command, type)
char *command, *type;
The arguments to popen are pointers to null-terminated strings contain-
ing 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.
A stream opened by popen should be closed by pclose, which waits for
the associated process to terminate and returns the exit status of the
Because open files are shared, a type "r" command may be used as an
input filter, and a type "w" as an output filter.
pipe(2), fopen(3S), fclose(3S), system(3), wait(2), sh(1)
Popen returns a null pointer if files or processes cannot be created,
or the shell cannot be accessed.
Pclose returns -1 if stream is not associated with a `popened' command.
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, for instance,
with fflush, see fclose(3).
Popen always calls sh, never calls csh.
18 July 1983 POPEN(3)