File existence test using variable

Question

I've got a variable that holds a path to a file as text. I want to test if the file in the path exists. The script below doesn't give the answer I expect. But if I delete the second line and put the path in quotes on the fourth line in place of fpath it works.
I am using applescript to get the path from the body of an email. That works fine and I can act on the path in applescript (attaching the specified file to an email). I just can't get the existence test to work. Any help?
set msg to "no"
set fpath to "/path/filename"
tell application "Finder"
if exists POSIX file fpath then
set msg to "yes"
end if
end tell
display dialog msg

Answer 1

The finder has a hard time with POSIX paths. It's much happier dealing with aliases. If you're dealing with aliases, though, you can avoid the Finder altogether:
set msg to "no"
set fpath to "/etc/hosts"
try
  set p to POSIX file fpath as alias
  set msg to "yes"
end try
display dialog msg
The idea here is that the coercion of the POSIX file to an alias will fail if the path doesn't resolve. Putting this inside a try block ensures that you fail gracefully and never get to set msg to "yes".