set dash_ to (ASCII character 45)
set d to text item delimiters
set text item delimiters to "/"
set f to (POSIX path of (path to me))'s text 1 thru text item -3 & "/"
set text item delimiters to d
do shell script ("cd /" & quoted form of f & "; sass " & dash_ & dash_ & "watch style.scss:style.css")

set dash_ to (ASCII character 45)
set d to text item delimiters
set text item delimiters to "/"
set f to (POSIX path of (path to me))'s text 1 thru text item -3 & "/"
set text item delimiters to d
--do shell script (f & "sass " & dash_ & dash_ & "watch style.scss:style.css")
display dialog (f)
do shell script ("cd /" & f & "; sass " & dash_ & dash_ & "watch style.scss:style.css")

http://macscripter.net/viewtopic.php?id=16755

Run terminal/script/shell command in the script\'s parent folder

script, directory, terminal

AppleScript