This isn't really possible, you can't rely the data being available by the
time you want to check if there is data to read. This is a race condition
that can only really be solved by putting in a timeout, which sucks.
testing if you have a tty is quite a common way to work around the issue
Thanks Steve
On Thu, Nov 21, 2013 at 2:43 AM, David Adam <zanc...@ucc.gu.uwa.edu.au>wrote:
> On Wed, 20 Nov 2013, Marcin Zajączkowski wrote:
> > I'm porting a script from bash to fish which reads stdin and I have a
> > problem with determining if there is anything to read from stdin or (n
> > the other case) input should be fetched from call params.
> >
> > There is in the original script:
> > # If no tty, data should be available on stdin
> > if ! [[ "$( tty )" == /dev/* ]]; then
> > input="$(< /dev/stdin)"
> > # Else, fetch input from params
> > else
> > input="$*"
> > fi
> >
> > and in fact when used after pipe it returns "not a tty". In fish it
> > works fine for a simple execution:
> > $ echo "aaa" | tty
> > not a tty
> >
> > but when tty is called within my function it always returns /dev/pts/*.
>
> This mirrors the behaviour of your function above:
>
> ```
> function myfunc
> if not tty >/dev/null
> read input
> else
> set input $argv
> end
> echo $input
> end
> ```
> zanchey@motsugo ~> myfunc 1 2 3
> 1 2 3
> zanchey@motsugo ~> echo aaa | myfunc
> aaa
>
> > How can I determine that my function has something to on read stdin (to
> > not call "read" then which would open an interactive prompt)?
>
> This is a different question; the tty function does not check for the
> presence or absence of data on stdin. I don't actually know of a clever
> way of doing this from a shell script; in C I guess you'd do a select()
> with a zero timeout or something.
>
> David Adam
> zanc...@ucc.gu.uwa.edu.au
>
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