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Full Discussion: Getting piped input from a program that's buffering it's stdout
Top Forums Shell Programming and Scripting Getting piped input from a program that's buffering it's stdout Post 302982931 by Juha Nurmela on Tuesday 4th of October 2016 06:41:11 PM
Old 10-04-2016
I didn't, it's
Code:
 $ time btpick audio_.
audio_1
    0.01s real     0.00s user     0.00s system

as-is

---------- Post updated at 01:25 AM ---------- Previous update was at 01:24 AM ----------

not very pretty, but must do, this time
Code:
ping="l2ping -fc1 -a "

for i in `sed -n "s/.* \($1\).*/\1/p" /etc/bluetooth/hosts`
do
        exec 2>&1
        $ping "$i" & (sleep 1; exec $ping "$i") &

done | sed -n '/.* from \(.*\) seq.* result=0 $/ {
        s//\1/p
        q
}
'

---------- Post updated at 01:41 AM ---------- Previous update was at 01:25 AM ----------

Tried it quickly, setting $i in the loop into something nonexisting, to force an error message. It all works okay, after all, without the 2>.

The interactive shell is just waiting for the script to end, and the shell running the script is non-interactive. It's children, the pingers, can freely write to stderr even when it's a terminal, they are not in background, job control-wise. Removing the redirection of the stderr, nice to not be hiding error messages.

Treppenwitz:

expect -c 'spawn prog; interact'seems to do what I was after.
Last edited by Juha Nurmela; 10-07-2016 at 02:29 PM.. Reason: slow cogs
 

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LEARN ABOUT OPENSOLARIS

setlinebuf

setbuffer(3C)						   Standard C Library Functions 					     setbuffer(3C)

NAME

       setbuffer, setlinebuf - assign buffering to a stream

SYNOPSIS

       #include <stdio.h>

       void setbuffer(FILE *iop, char *abuf, size_t asize);

       int setlinebuf(FILE *iop);

DESCRIPTION

       The  setbuffer()  and  setlinebuf()  functions  assign  buffering to a stream. The three types of buffering available are unbuffered, block
       buffered, and line buffered. When an output stream is unbuffered, information appears on the destination file or terminal as soon as  writ-
       ten;  when  it  is  block  buffered, many characters are saved and written as a block; when it is line buffered, characters are saved until
       either a NEWLINE is encountered or input is read from stdin. The fflush(3C) function may be used to force the block out early. Normally all
       files  are  block buffered. A buffer is obtained from malloc(3C) upon the first getc(3C) or putc(3C) performed on the file. If the standard
       stream stdout refers to a terminal, it is line buffered. The standard stream stderr is unbuffered by default.

       The setbuffer() function can be used after a stream iop has been opened but before it is read or written. It uses the character array  abuf
       whose  size  is	determined  by the asize argument instead of an automatically allocated buffer.  If abuf is the null pointer, input/output
       will be completely unbuffered. A manifest constant BUFSIZ, defined in the <stdio.h> header, tells how large an array is needed:

       char buf[BUFSIZ];

       The setlinebuf() function is used to change the buffering on a stream from block buffered or  unbuffered  to  line  buffered.  Unlike  set-
       buffer(), it can be used at any time that the stream iop is active.

       A  stream  can  be  changed  from  unbuffered  or  line buffered to block buffered by using freopen(3C). A stream can be changed from block
       buffered or line buffered to unbuffered by using freopen(3C) followed by setbuf(3C) with a buffer argument of NULL.

RETURN VALUES

       The setlinebuf() function returns no useful value.

SEE ALSO

       malloc(3C), fclose(3C), fopen(3C), fread(3C), getc(3C), printf(3C), putc(3C), puts(3C), setbuf(3C), setvbuf(3C)

NOTES

       A common source of error is allocating buffer space as an "automatic" variable in a code block, and then failing to close the stream in the
       same block.

SunOS 5.11							    13 May 1997 						     setbuffer(3C)
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