[TxMt] how to use html preview for LaTeX in TM1

[Piero D'Ancona]

I'm confident this is a stupid question but I'm stymied, as someone would say.

I would like to experiment with using the feature
'pipe through command' of the html preview in TM1
in combination with pdflatex.

1) I created a folder /Users/piero/Desktop/prova

2) in the folder there's a trivial latex file prova.tex, which
compiles just fine producing a pdf of one page

3) I added a file script.sh which contains the following:

if /usr/texbin/pdflatex -output-directory /User/piero/Desktop/prova 
-interaction=nonstopmode 
/dev/stdin; then
    echo '<meta http-equiv="refresh" content="0; tm-file:///tmp/stdin.pdf">'
fi

(this approach is suggested in Allan's blog. The script file
has been suitably chmodded)

4) in the html preview window of TM I checked the button
'Pipe text through' and added the path to
/Users/piero/Desktop/prova/script.sh

5) But, when I invoke web preview, the html window shows only

This is pdfTeX, Version 3.1415926-2.3-1.40.12 (TeX Live 2011) 
restricted \write18 enabled. 
entering extended mode ! I can't write on file `stdin.log'. (Press 
Enter to retry, or Control-D 
to exit; default file extension is `.log') Please type another 
transcript file
name ! Emergency stop ! ==> Fatal error occurred, no output PDF file 
produced!


What am I doing wrong? is this some permission issue in Lion
10.7.2 which I'm using? 

Bonus question: in view of TM2 (thanks Allan - never lost the
faith), am I just wasting time since the feature will not work
in the future?

Thanks for help
Piero