So, this version works:
cat /dev/stdin > /tmp/stdin.tex if pdflatex -output-directory /tmp -interaction=nonstopmode /tmp/stdin.tex; then echo '<meta http-equiv="refresh" content="0; file:///tmp/stdin.pdf">' fi
If you pipe through this script you get a live preview of the pdf file every time you modify the document (no need to save). For a one-page document it is quite nice. Unfortunately, the live preview comes back to the beginning after each compilation, which is less than convenient for longer documents and essentially defeats the purpose. If it were possible to let the view to stay on the same page after each compilation, this would make a serious alternative to other workflows (and self contained inside TM, to boot)
Piero