04-30-2015
There's an instant between 'check' and 'create file' when something else could create that file without bash knowing.
You could use mkdir. That's atomic. The first time it gets called it succeeds and creates the folder, the second time, it fails, nothing can sneak between.
I think there's a way for bash to try and create a file and report error if it already exists but am struggling to find the syntax.
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wait(1) General Commands Manual wait(1)
NAME
wait - await process completion
SYNOPSIS
[pid]
DESCRIPTION
If no argument is specified, waits until all processes (started with of the current shell have completed, and reports on abnormal termina-
tions. If a numeric argument pid is given and is the process ID of a background process, waits until that process has completed. Other-
wise, if pid is not a background process, exits without waiting for any processes to complete.
Because the system call must be executed in the parent process, the shell itself executes without creating a new process (see wait(2)).
Command-Line Arguments
supports the following command line arguments:
The unsigned decimal integer process
ID of a command, whose termination is to wait for.
WARNINGS
Some processes in a 2-or-more-stage pipeline may not be children of the shell, and thus cannot be waited for.
SEE ALSO
csh(1), ksh(1), sh-posix(1), sh(1), wait(2).
STANDARDS CONFORMANCE
wait(1)