In 73e06b9d4c (bash.bashrc: Update PS1 if PS1 wasn't exported. Closes
#653, 2016-07-14), we updated `/etc/bash.bashrc` to avoid overriding
`PS1`, but the way it was done requires `cut.exe` to be in the `PATH`.
Now, while _most_ of the time we're running inside a login Bash where
the `PATH` has been appropriately modified, sometimes we don't. In that
case, `cut.exe` is not in the `PATH`.
We should not spawn a new process, anyway, as spawning processes is
really expensive in the MSYS2 runtime because of all the contortions
necessary to emulate the POSIX syscall `fork()`.
Let's just avoid that extra process by using `case`, which is a Bash
built-in and therefore won't cost much time to run.
This fixes https://github.com/git-for-windows/git/issues/3652
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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