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POPEN(3S) POPEN(3S) NAME popen, ppopen, vepopen, pclose - open a pipe to/from a process SYNOPSIS #include <stdio.h> FILE *popen(command, type) char *command, *type; FILE *ppopen(command, type) char *command, *type; FILE *vepopen(command, type, args, env) char *command, *type, **args, **env; int pclose(stream) FILE *stream; DESCRIPTION The first argument to popen is a pointer to a null-terminated string containing a command line for sh(1). Type is as in fopen(3). Popen creates a pipe between the calling process and the command and returns a stream pointer that can be used to write to the standard input of the command or to read from the standard output. Ppopen uses the -p shell flag to restrict the environment of the shell. Both popen and ppopen set the effective userid to the real userid be- fore calling the shell. Vepopen has arguments akin to those of execve (see exec(2)): a file to be executed, a mode as above, a null-terminated vector of argument strings, and a null-terminated vector of environment strings. The shell is not called, and the effective userid is preserved. A stream opened by these routines should be closed by pclose, which waits for the associated process to terminate and returns the exit sta- tus of the command. Because the command inherits open files, in particular standard input and output, a type "r" call may be used to insert a filter in the in- put, and type "w" in the output. SEE ALSO exec(2), pipe(2), fopen(3), stdio(3), system(3) DIAGNOSTICS Popen returns a null pointer if files or processes cannot be created, or the Shell cannot be accessed. Pclose returns -1 if there is no process to wait for. BUGS 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 calling fflush; see fopen(3). The resetting of the userid is probably gratuitous; it is there as a defense against incautious use of the routine by set-uid programs. I/O type "r+w" exists but is not useful. POPEN(3S)