|Linux / Unix Command: popen|
NAMEpopen, pclose - process I/O
FILE *popen(const char *command, const char *type);
DESCRIPTIONThe popen() function opens a process by creating a pipe, forking, and invoking the shell. Since a pipe is by definition unidirectional, the type argument may specify only reading or writing, not both; the resulting stream is correspondingly read-only or write-only.
The command argument is a pointer to a null-terminated string containing a shell command line. This command is passed to /bin/sh using the -c flag; interpretation, if any, is performed by the shell. The mode argument is a pointer to a null-terminated string which must be either `r' for reading or `w' for writing.
The return value from popen() is a normal standard I/O stream in all respects save that it must be closed with pclose() rather than fclose(). Writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the process that called popen(), unless this is altered by the command itself. Conversely, reading from a ``popened'' stream reads the command's standard output, and the command's standard input is the same as that of the process that called popen.
Note that output popen streams are fully buffered by default.
RETURN VALUEThe popen function returns NULL if the fork(2) or pipe(2) calls fail, or if it cannot allocate memory.
ERRORSThe popen function does not set errno if memory allocation fails. If the underlying fork() or pipe() fails, errno is set appropriately. If the mode argument is invalid, and this condition is detected, errno is set to EINVAL.
SEE ALSOfork(2), sh(1), pipe(2), wait4(2), fflush(3), fclose(3), fopen(3), stdio(3), system(3)
Important: Use the man command (% man) to see how a command is used on your particular computer.