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Minix/CD-ROM-2.0/MINIX/MANUALS/MAN3/POPEN.3

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+.\"	@(#)popen.3	6.1 (Berkeley) 5/15/85
+.\"
+.TH POPEN 3 "May 15, 1985"
+.AT 3
+.SH NAME
+popen, pclose \- initiate I/O to/from a process
+.SH SYNOPSIS
+.nf
+.ft B
+#include <stdio.h>
+
+FILE *popen(const char *command, const char *type)
+int pclose(FILE *stream)
+.SH DESCRIPTION
+The arguments to 
+.B 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.  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.
+.PP
+A stream opened by
+.B popen
+should be closed by
+.BR pclose ,
+which waits for the associated process to terminate
+and returns the exit status of the command.
+.PP
+Because open files are shared, a type "r" command may be used as an input
+filter, and a type "w" as an output filter.
+.SH "SEE ALSO"
+.BR pipe (2),
+.BR fopen (3),
+.BR fclose (3),
+.BR system (3),
+.BR wait (2),
+.BR sh (1).
+.SH DIAGNOSTICS
+.B Popen
+returns a null pointer if files or processes cannot be created, or the shell 
+cannot be accessed.
+.SH 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 careful buffer flushing, for instance, with
+.BR fflush ,
+see
+.BR fclose (3).