popen(3S) DG/UX R4.11MU05 popen(3S)
NAME
popen, pclose - initiate pipe to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(const char *command, const char *type);
int pclose(FILE *stream);
DESCRIPTION
popen creates a pipe between the calling program and the command to
be executed. The arguments to popen are pointers to null-terminated
strings. command consists of a shell command line. type is an I/O
mode, either r for reading or w for writing. The value returned is a
stream pointer such that one can write to the standard input of the
command, if the I/O mode is w, by writing to the file stream [see
intro(3)]; and one can read from the standard output of the command,
if the I/O mode is r, by reading from the file stream.
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 command.
Because open files are shared, a type r command may be used as an
input filter and a type w as an output filter.
Errors
popen returns a null pointer if files or processes cannot be created.
pclose returns -1 if stream is not associated with a popened command
or waitpid (used in the implementation of pclose) returns a -1 for
some reason (see NOTICES below).
Considerations for Threads Programming
+---------+-----------------------------+
| | async- |
|function | reentrant cancel cancel |
| | point safe |
+---------+-----------------------------+
|pclose | N - - |
|popen | N - - |
+---------+-----------------------------+
USAGE
Here is an example of a typical call:
#include <stdio.h>
#include <stdlib.h>
main()
{
char *cmd = "/usr/bin/ls *.c";
char buf[BUFSIZ];
FILE *ptr;
if ((ptr = popen(cmd, "r")) != NULL)
while (fgets(buf, BUFSIZ, ptr) != NULL)
(void) printf("%s", buf);
return 0;
}
This program will print on the standard output [see stdio(3S)] all
the file names in the current directory that have a .c suffix.
REFERENCES
pipe(2), waitpid(2), reentrant(3), fclose(3S), fopen(3S), stdio(3S),
system(3S)
NOTICES
If the original and popened processes concurrently read or write a
common file, neither should use buffered I/O. Problems with an
output filter may be forestalled by careful buffer flushing, for
example, with fflush [see fclose(3S)].
If SIGCHLD is set to SIG_IGN, pclose will return a -1 with errno set
to ECHILD (the results of calling waitpid).
A security hole exists through the IFS and PATH environment
variables. Full pathnames should be used (or PATH reset) and IFS
should be set to space and tab
(" \t").
Licensed material--property of copyright holder(s)