Applescript do shell to create file with text and manipulate - shell

Question

I am trying to write a simple logger with Applescript. I have a couple of questions
Firstly I am testing if a file exists, if it does not I want to create a file with that name and set the first line to a string "Counter:0".
So far I have this but my syntax is wrong. Appreciate any help as the info on the web is a bit slender.
tell application "Finder"
set thePath to "/Data/GameLog/"
set theFile to thePath & (do shell script "date '+%Y.%m.%d'" & ".log")
if exists POSIX file thePath then
--display dialog "Found"
else
do shell script "Counter:0" > echo thePath
end if
end tell
secondly I would like to read the first line of the file (ie Counter:0) and increment the integer after the : by 1.
Help v.much appreciated

Answer 1

Based on vadian's answer:
set logFolder to (POSIX path of (path to home folder)) & "Desktop/" -- the trailing slash is crucial
set timeStamp to do shell script "date '+%Y.%m.%d'"
set logFile to logFolder & timeStamp & ".log"
if ((do shell script "test -d " & quoted form of logFolder & "&& echo true||echo false") as boolean) then
try
close access logFile
end try
try
set fileReference to open for access logFile with write permission
on error
display alert "File already open"
return -1
end try
set counter to (get eof of fileReference)
if counter is not 0 then
try
set counter to (read fileReference from 9) as integer
on error
close access logFile
display alert "Read error"
return -1
end try
set counter to counter + 1
set eof of fileReference to 0
end if
write ("Counter:" & counter) to fileReference as «class utf8»
close access logFile
else
display alert "Folder does not exist"
end if
The advantage is that this will not ignore errors. It will also be able to find your home directory without needing you to manually enter it in code. This is safe since we check for the logFolder first. The rest of the code can't fail if that folder exists. I am aware that AppleScript has a method for checking whether or not a file exists, but I have found that functionality to be fairly difficult to use when dealing with POSIX paths, so I'm using a do shell script instead, which naturally deals with POSIX paths.

Answer 2

Please try this, change the file path in the first line (consider the trailing slash)
set logFolder to "/Users/myUser/Desktop/" -- the trailing slash is crucial
set timeStamp to do shell script "date '+%Y.%m.%d'"
set logFile to logFolder & timeStamp & ".log"
try
set fileReference to open for access logFile with write permission
set counter to (get eof of fileReference)
if counter is not 0 then
set counter to read fileReference from 9
set counter to counter + 1
set eof of fileReference to 0
end if
write ("Counter:" & counter) to fileReference as «class utf8»
close access fileReference
on error
try
close access logFile
end try
end try