In dos you can redirect all of std{in,out,err} by creating a batch file like 

@echo off
stty update.txt
ppm update
stty con

[download]
I understand that ppm update does not simply write to stderr, but you could still try if this works.

(This is the only way to redirect error messages to nul in dos as command does not have a redirect operator to redirect stderr.)

In reply to Re: Redirect filtered PPM screen output to a file. by ambrus
in thread Redirect filtered PPM screen output to a file. by davido

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