add directory Minix

Minix/1.7.5/MANUALS/CAT3/POPEN.3

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+NAME
+	  popen, pclose	- initiate pipe	to/from	a process
+SYNTAX
+	  #include <stdio.h>
+	  FILE *popen (command,	type)
+	  char *command, *type;
+	  int pclose (stream)
+	  FILE *stream;
+DESCRIPTION
+	  The arguments	to popen are pointers to null-terminated
+	  strings containing, respectively, a shell command line and
+	  an I/O mode, either r	for reading or w for writing.  Popen
+	  creates a pipe between the calling program and the command
+	  to be	executed.  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; 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.
+SEE ALSO
+	  pipe(2), wait(2), fclose(3S),	fopen(3S), system(3S).
+DIAGNOSTICS
+	  Popen	returns	a NULL pointer if files	or processes cannot be
+	  created, or if the shell cannot be accessed.
+	  Pclose returns -1 if stream is not associated	with a
+	  ``popened'' command.
+BUGS
+	  If the original and ``popened'' processes concurrently read
+	  or write a common file, neither should use buffered I/O,
+	  because the buffering	gets all mixed up.  Problems with an
+	  output filter	may be forestalled by careful buffer flushing,
+	  e.g. with fflush; see	fclose(3S).
+				  
+