Thursday 26 May 2016

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:


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.

Monday 16 May 2016

Update on old DisplayLink drivers

An update on my earlier post of 2012.

Driver 1.1.62 (15 May 2016) is now available at 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:


# 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     " Configured"
    Screen      0  "Screen0" 0 0
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"

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"

Section "Module"
    Load  "glx"

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

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

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

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

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