Created attachment 5438 
patch generated by git diff

The command line arguments "--help" and "--with-ck-launch" can't be used on systems which have a non-bash /bin/sh (e.g. Debian, as far as I'm aware). This is due to the use of "==" instead of "=" in test commands, which is a bash extension.

I discovered this with the "checkbashisms" perl script while switching my /bin/sh from bash to dash on Arch.

To verify (with dash installed):

DISPLAY=invalid  # Avoid actually launching xfce; this should prevent it
dash "$(which startxfce4)" --help

It should output usage information, but what it actually outputs is the following:

/usr/bin/startxfce4: 27: test: x--help: unexpected operator
/usr/bin/startxfce4: 40: test: x--help: unexpected operator
/usr/bin/startxfce4: X server already running on display invalid
xrdb: Can't open display 'invalid'
xfce4-session: Cannot open display: .
Type 'xfce4-session --help' for usage.