Playing around in my system, I stumbled upon
~$ echo $XDG_DATA_DIRS
/usr/share/ubuntustudio:/usr/share/xfce4:/usr/local/share:/usr/share:/var/lib/snapd/desktop:/usr/share
Asking myself why /usr/share is twice in the path I found out that the following snippet in
/etc/alternatinves/x-session-manager which is a link to /usr/bin/startxfce4 is responsible:
#!/bin/sh
.
.
.
if test "x$XDG_DATA_DIRS" = "x"
then
if test "x/usr/share" = "x/usr/local/share" -o "x/usr/share" = "x/usr/share"; then
XDG_DATA_DIRS="/usr/local/share:/usr/share"
else
XDG_DATA_DIRS="/usr/share:/usr/local/share:/usr/share"
fi
else
XDG_DATA_DIRS="$XDG_DATA_DIRS:/usr/share"
fi
export XDG_DATA_DIRS
.
.
.
When I look at the line
if test "x/usr/share" = "x/usr/local/share" -o "x/usr/share" = "x/usr/share"; then
I have difficulties to understand this if-statement, for me it looks like a comparison of strings where the first one is always false and the second one is always true.
Combined with a logical or the test always evaluates to true, so I could shorten the line to
if true; then or I could say I don't need an if-statement at all.
Where is my mistake? Or is it written like this to confuse beginners like me?