You need to create file /etc/openhab/html/lametric.json, adjust path according to File Locations.
Here is my rule:
val clear = "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"
//other base64 icons
rule "LaMetriс"
when Time cron "*/15 * * * * ?" //run every 15 seconds
then
//some your code
iconBase64 = clear
textOutTemp = YOURTEMP.replaceAll(".0°","°")
executeCommandLine(Duration.ofSeconds(6), "/bin/sh", "-c",
"(echo '
{
\"frames\": [
{
\"text\": \"" + textOutTemp + "\",
\"icon\": \"data:image/gif;base64," + iconBase64 + "\"
}
]
}
' > /etc/openhab/html/lametric.json) >/dev/null 2>&1; echo $?")
end