Gfilui

I was able to modify the login background in gnome3-desktop using the following script way back in Ubuntu 16.04 LTS.

#!/usr/bin/sh

if [ "$IMAGE" = "" ]; then
 IMAGE=$(
 dbus-launch gsettings get org.gnome.desktop.screensaver picture-uri |
 sed -e "s/'//g" |
 sed -e "s/^file:////g"
 )
fi
IMAGE="/home/chiku/Dropbox/LinuxStuff/Drow.jpg"

if [ ! -f $IMAGE ]; then
 echo "unknown IMAGE $IMAGE"
 exit 1
fi

echo ''
echo 'using the following image as login background:'
echo $IMAGE
echo ''

if [ -d ~/tmp ]; then
 CREATED_TMP="0"
else
 mkdir -p ~/tmp
 CREATED_TMP="1"
fi

WORKDIR=~/tmp/gdm-login-background
GST=/usr/share/gnome-shell/gnome-shell-theme.gresource
GSTRES=$(basename $GST)

mkdir -p $WORKDIR
cd $WORKDIR
mkdir theme

for r in `gresource list $GST`; do
 gresource extract $GST $r >$WORKDIR$echo $r 
done

cd theme
cp "$IMAGE" ./

echo "
#lockDialogGroup 
 background: #2e3436 url(resource:///org/gnome/shell/theme/$(basename $IMAGE));
 background-size: cover;
 background-repeat: no-repeat;
" >>gnome-shell.css

echo '<?xml version="1.0" encoding="UTF-8"?>
<gresources>
 <gresource prefix="/org/gnome/shell/theme">' >"$GSTRES.xml"
for r in `ls *.*`; do
 echo " <file>$r</file>" >>"$GSTRES.xml"
done
echo ' </gresource>
</gresources>' >>"$GSTRES.xml"

glib-compile-resources "$GSTRES.xml"

sudo cp "/usr/share/gnome-shell/$GSTRES" "/usr/share/gnome-shell/$GSTRES.backup"
sudo cp "$GSTRES" /usr/share/gnome-shell/

rm -r $WORKDIR

if [ "$CREATED_TMP" = "1" ]; then
 rm -r ~/tmp
fi

But the sed command give errors while trying to do the same in the native installation of gnome3 in Ubuntu 18.04.

Do any of you know how to solve it??

Any help is appreciated.