On Fri, 14 Mar 2003 09:35:55 +0200
shlomo solomon <[EMAIL PROTECTED]> wrote:
> So what's my problem? It seems that both the above solutions are writing to a
> buffer and the actual screen output is not immediate, but in spurts.
That's a result of stdio default behaviour. Each application can
control its buffering behaviour via setvbuf(3) to one of three
possible modes:
- Unbuffered: every call to stdio (printf, puts, putchar,
etc.) is passed to write(2).
- Fully buffered: Only when a buffer (programmer specified
size) is filled, write(2) is called.
- Line buffered: If a linefeed character is written (or
buffer is full), write(2) is called.
The defaults are:
- STDERR: unbuffered
- STDOUT: line buffered if it's connected to tty device,
fully buffered otherwise.
So, by default, if you pipe the output (or redirect it to a file)
the output from STDOUT will be fully buffered.
If your script is written in perl, than look in perldoc perlvar
for the special variable $| (dollar-pipe), it would give you
partial control over your output buffering. There isn't any
such control mechanism for the shell (maybe bash has some extra
feature -- anybody?).
This won't help you with grep, or any other precompiled application,
which raises an interesting question --
Maybe we need a general mechanism to control this default behaviour
(when the application itself does not specify the buffering). Since
this is done in stdio library the obvious solution would be via
some new environment variable. E.g:
env "STDIO_BUFFER=all:buffered,1=unbuffered" foo | bar | geek
Cheers,
----------------------------------------------------------------
Oron Peled Voice/Fax: +972-4-8228492
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- Larry Wall.
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