HOWTO determine if a command in a pipeline has ended.

[rikky]

Hello

The quest is HOW to know if a program in a pipe, that feeds its output to your baconprogram has ended?

For example I have this function :

FUNCTION GET_STDIN$()
 
 LOCAL string$
 LOCAL STDIN
 
 WHILE TRUE
   STDIN = WAIT(STDIN_FILENO, 50)
   IF STDIN = 0 THEN BREAK
   string$ = string$ & CHR$(STDIN)
 WEND
 
 RETURN string$
 
END FUNCTION
which I use in my program, lets call it PRINT_STDIN.bac

WHILE TRUE
 string$ = CHOP$(GET_STDIN$())
 IF string$ = "" THEN CONTINUE
 PRINT string$
WEND
And I have another program, lets call it FEED_STDIN.bac

PRINT "hallo baconworld."
SLEEP 3000
PRINT "dag baconworld."
So if I do on the commandline :

FEED_STDIN | PRINT_STDIN
Then it does the job.

It prints "hallo baconworld.", sleeps 3 seconds, and then it prints "dag baconworld.".
And then it waits forever for new input.

But FEED_STDIN has ended.

HOW ?? to determine that the feeding program has ended?
I've searched the internet for years, looking for a solution.
Now I've got it.

STDIN = WAIT(STDIN_FILENO, 50)
returns immediately, if there is no input anymore.
It does not wait 50 miliseconds.

So my new program becomes:

GLOBAL EOI  : ' END OF INPUT

FUNCTION GET_STDIN$()
 
 LOCAL string$
 LOCAL STDIN
 LOCAL iter
 
 EOI = 0
 
 WHILE TRUE
   iter = TIMER
   STDIN = WAIT(STDIN_FILENO, 50)
   IF STDIN = 0 THEN
     IF TIMER - iter < 2 THEN EOI = 1
     BREAK
   END IF
   string$ = string$ & CHR$(STDIN)
 WEND
 
 RETURN string$
 
END FUNCTION

WHILE TRUE
 string$ = CHOP$(GET_STDIN$())
 IF string$ = "" THEN
   IF EOI THEN END 0
   CONTINUE
 END IF
 PRINT string$
WEND

And now it does the job as it should.

 Rik.

[Pjot]

Thanks rikky,

The WAIT function, which is based on the libc select function, indeed is often overseen.

In combination with STDIN_FILENO it can be a very powerful function to process input from stdin. The internal BaCon editor also uses the WAIT function heavily for this purpose.

Best regards
Peter