Re: using gnuplot as a filter

[<P...@dr...>]

Hans-Bernhard Br=C3=B6ker wrote:
> P=C3=A1draig Brady wrote:
>> I tried to get a gnuplot script to read
>> from stdin like a normal linux filter using plot '-'
>=20
>> I know how to work around this but it's a horrible hack.
>> I.E. rather than:
>>   gen_data | ./plot.gp > file.png
>=20
> Without seeing what's in plot.gp, it's quite unclear what you're trying
> to do here.  What's wrong with the more conventional
>=20
>     gen_data | gnuplot plot.gp > file.png

I want to read data on stdin and write png to stdout.
I.E. behave like a standard unix filter which has lots of advantages.
Here is an example plot.gpi script to do that:

#!/usr/bin/env gnuplot
set term png
plot '-'

However it doesn't work as shown below, as gnuplot drains its stdin on st=
artup
as detailed previously. It should not do that if possible. At least it sh=
ould
be a runtime rather than a compile time decision. Your variation above is=
 equivalent.

$ seq 10 | ./plot.gpi > plot.png
plot '-'
"./plot.gpi", line 3: warning: Skipping data file with no valid points

If you write the data to stdin after the plot command, then it works:
(cat ./plot.gpi; seq 10) | gnuplot > plot.png

Ethan's variant here is not as general as it hardcodes the
source of the data within the script

echo 'plot "< seq 10"' | GNUTERM=3Dpng gnuplot > plot.png

thanks,
P=C3=A1draig.