Parsing paths & deleting empty items from a bash list

This spell will split a path into directories:

IFS=/ read -d "" -r -a path <<<"$path"

but because of the action of <<<, the final item will have a newline appended -- but that can be removed thus:

path[-1]="${path[-1]%$'\n'}"

If the path began with a /, then path[0] will be empty, so as the leading / is important, we'll recover that

test -z "${path[0]}" && path[0]="/"

This spell will remove empty items from the list (and also renumber the indexes):

IFS= eval 'path=(${path[@]})'

(We could avoid the eval by saving IFS, but eval is safe enough here not to bother).

Now it is simple enough to iterate over "${path[@]}" and perform a chdir on each stage.

Update on old DisplayLink drivers

An update on my earlier post of 2012.

Driver 1.1.62 (15 May 2016) is now available at http://www.displaylink.com/downloads/ubuntu and does not require any fixups for wrong USB vendor ID numbers, or patches for kernels > 4.5.0

For my HP displaylink hub I have:

/etc/udev/rules.d/50-displaylink.rules:

# DisplayLink devices always have the active configuration on configuration #1
ATTR{idVendor}=="17e9", ATTR{idProduct}=="01d4", RUN+="/usr/bin/dlconfig"

and /usr/bin/dlconfig:

#! /bin/bash

echo 1 > "/sys/$DEVPATH/bConfigurationValue"

However, I must insert the USB device AFTER logging into to X or I get two fb devices added, one owned by udl and one by evdi. I suspect this is a race condition problem.

In any case, none of it works for me -- I'm not able to view anything at all on the frame buffer. I guess my USB device is too old.

However, if I modprobe udlfb and ignore the evdi drivers, and udl then I at least get a working framebuffer that can display images with fbi. -- but the colour depth is stuck at 16.

I'm able to use it as a primary device for an X11 session with this /etc/X11/xorg.conf

Section "ServerLayout"
    Identifier     "X.org Configured"
    Screen      0  "Screen0" 0 0
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
    ModulePath   "/usr/lib/xorg/modules"
    FontPath     "/usr/share/fonts/X11/misc"
    FontPath     "/usr/share/fonts/X11/cyrillic"
    FontPath     "/usr/share/fonts/X11/100dpi/:unscaled"
    FontPath     "/usr/share/fonts/X11/75dpi/:unscaled"
    FontPath     "/usr/share/fonts/X11/Type1"
    FontPath     "/usr/share/fonts/X11/100dpi"
    FontPath     "/usr/share/fonts/X11/75dpi"
    FontPath     "built-ins"
EndSection

Section "Module"
    Load  "glx"
EndSection

Section "InputDevice"
    Identifier  "Keyboard0"
    Driver      "kbd"
EndSection

Section "InputDevice"
    Identifier  "Mouse0"
    Driver      "mouse"
    Option        "Protocol" "auto"
    Option        "Device" "/dev/input/mice"
    Option        "ZAxisMapping" "4 5 6 7"
EndSection

Section "Monitor"
    Identifier   "Monitor0"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Device"
    Identifier  "Card1"
    Driver    "fbdev"
    BusID    "USB"
    Option    "fbdev"    "/dev/fb1"
    Option    "ReportDamage"    "true"
EndSection

Section "Screen"
    Identifier "Screen0"
    Device     "Card1"
    Monitor    "Monitor0"
    DefaultDepth    16
    SubSection "Display"
        Viewport   0 0
        Depth     1
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     4
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     8
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     15
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     16
    EndSubSection
EndSection