How can I create or replace a file using Applescript? - macos

Question

I'm trying to write content to a file, /tmp/test.txt with AppleScript.
If the file doesn't exist, I want to create it.
If it does exist, I want to replace the contents.
This is proving quite difficult because AppleScript has a different syntax for creating a new file versus writing to an existing file. I also thought about deleting a file if it already exists, and then creating it, but AppleScript will move things to the trash by default and so even that is rather complicated.
The data I am going to write to the file may have a lot of special characters in it, so I don't really want to do something like do shell script "cat " + data + " > /tmp/txt.txt" because I am unaware of any escapeshellarg for AppleScript.
Below is what I have so far but I'm getting an error:
Can't make file "Macintosh HD:private:tmp:test.txt" into type reference.
I would really like to abstract this by improving the helper function write_to_file that I got here so that it would take care of creating the file if it does not exist.
my write_to_file("hello", "/tmp/test.txt", false)
on write_to_file(this_data, target_file, append_data)
try
if not (exists POSIX file target_file) then
make new document file at ("/tmp/" as POSIX file as alias) with properties {name:"test.txt", text:the_data}
end if
set the target_file to the target_file as POSIX file
set the open_target_file to open for access file target_file with write permission
if append_data is false then set eof of the open_target_file to 0
write this_data to the open_target_file starting at eof
close access the open_target_file
return true
on error e
try
display dialog e
close access file target_file
end try
return false
end try
end write_to_file
How can I create or replace a file using Applescript?

Answer 1

The first mistake you've made is mixing POSIX paths with HFS paths. A posix path is /tmp/test.txt and a hfs path to the same file will be Macintosh HD:tmp:test.txt if the name of the boot volume is Macintosh HD of course.
open for access file "Volume:Path:to:file.txt"
The second mistake is that for Mac OS X the /tmp folder is not the place to store temporary files. You will need administrator privileges to write there and the user will be prompted for username and password. It is stored in /var/folders and there is a folder created at login for each user, also with fast user switching. To access the path to this folder you should use the command path to temporary items. Temporary items will be removed between startups.
set theFile to (path to temporary items as string) & "test.txt"
The third mistake is that when you're using quoted form of you can use do shell script. Since AppleScript is unicode like the shell there is no such thing as that characters can't be handled by do shell script.
do shell script "/bin/echo -n " & (quoted form of "$#%^&*()#") & " > " POSIX path of theFile
At last you've made the mistake that you need to check for existence of a file. When you're using open for access command the file will be created when it doesn't exists for you. So the only code you need is:
set theFile to (path to temporary items as text) & "test.txt"
writeToFile(theFile, "Hello!", false)
writeToFile(theFile, (linefeed & "Goodbye!" as string), true)
on writeToFile(p, d, a)
try
set fd to open for access file p with write permission
if not a then set eof of fd to 0
write d to fd starting at (get eof of fd) as «class utf8»
close access fd
on error
close access file p
end try
end writeToFile
or using a do shell script which creates an UTF-8 file as well but the given path needs to be an POSIX path now
set theFile to (path to temporary items as text) & "test.txt"
writeToFile(POSIX path of theFile, "goodbye!", false)
writeToFile(POSIX path of theFile, (linefeed & "hello!" as string), true)
on writeToFile(p, d, a)
set cmd to "/bin/echo -n " & quoted form of d & " >"
if a then set cmd to cmd & ">"
do shell script cmd & space & quoted form of p
end writeToFile
Choose the one to your likings

Answer 2

Try:
my write_to_file("hello", "/tmp/test.txt", true)
on write_to_file(this_data, target_file, append_data)
try
tell application "System Events" to exists file target_file
if not the result then do shell script "> " & quoted form of target_file
set the open_target_file to open for access target_file with write permission
if append_data is false then set eof of the open_target_file to 0
write this_data to the open_target_file starting at eof
close access the open_target_file
return true
on error e
try
display dialog e
close access target_file
end try
return false
end try
end write_to_file