atomic create file if not exists from bash script
bash, c, linux
Solution
A 100% pure bash solution:
set -o noclobber
{ > file ; } &> /dev/null
This command creates a file named `file` if there's no existent file named `file`. If there's a file named `file`, then do nothing (but return a non-zero return code).
Pros of `>` over the `touch` command:
- Doesn't update timestamp if file already existed
- 100% bash builtin
- Return code as expected: fail if `file` already existed or if `file` couldn't be created; success if `file` didn't exist and was created.
Cons:
- need to set the `noclobber` option (but it's okay in a script, if you're careful with redirections, or unset it afterwards).
I guess this solution is really the bash counterpart of the `open` system call with `O_CREAT | O_EXCL`.
Problem
In system call `open()`, if I open with `O_CREAT | O_EXCL`, the system call ensures that the file will only be created if it does not exist. The atomicity is guaranteed by the system call. Is there a similar way to create a file in an atomic fashion from a bash script? UPDATE: I found two different atomic ways - Use set -o noclobber. Then you can use > operator atomically. - Just use mkdir. Mkdir is atomic