emf term with output "|cat >graph.emf" get wrong file

[fanuq]

use emf term and output use pipe get wrong file.
use the following command, get aa.emf, and ab.emf. aa.emf be ok.
ab.emf can't show the graph.
compare these two file, there was different.

set term emf
set output "aa.emf"
plot sin(x)
set output #save file
set output "|cat ab.emf"
plot sin(x)
set output #save file

how can I use pipe mode.
such as set output "|cat ab.emf" to get the right emf file.
thanks.

[Ethan Merritt]

emf output cannot be piped because the driver uses fseek().

[fanuq]

is there any method to use this term efficient.
as i plot the graph, graph show immediately