Concat in mqtt topic variable plus text

[domingopdf]

Hi, I'm trying to publish and subscribe on several topics that have the same first part. I include this first part in a subflow using a variable. I am not able to add the final part of the topic. For example, I want the following themes:
MicrodesysRed/f/entradasDig
MicrodesysRed/f/salidasDig

Consulting the forum and the internet and I saw that it should be written as:

&{mqtt_topic} & "entriesDig"

where mqtt_topic = MicrodesysRed/f/
But it does not work. The variable does recognize it well.

I leave here the screenshots of the creation of the variable and the topic

Thank you very much and greetings

[E1cid]

Hi.

You can leave the topic blank and create it in a prior node, and pass the topic in msg.topic
e.g

[{"id":"aa026e7dddedecc7","type":"subflow","name":"Subflow 1","info":"","category":"","in":[{"x":180,"y":120,"wires":[{"id":"9ab78c8c6e46d6b1"}]}],"out":[],"env":[{"name":"mqtt_topic","type":"str","value":"MicrodesysRed/f/","ui":{"label":{"en-US":"mqtt topic"},"type":"input","opts":{"types":["str","bool"]}}},{"name":"mqtt_end","type":"str","value":"test","ui":{"label":{"en-US":"mqtt ebd"},"type":"input","opts":{"types":["str"]}}}],"meta":{},"color":"#DDAA99"},{"id":"2b7f30fc05ca40a2","type":"mqtt out","z":"aa026e7dddedecc7","name":"","topic":"","qos":"","retain":"","respTopic":"","contentType":"","userProps":"","correl":"","expiry":"","broker":"e8ba3ef5.22f4a8","x":550,"y":120,"wires":[]},{"id":"9ab78c8c6e46d6b1","type":"change","z":"aa026e7dddedecc7","name":"","rules":[{"t":"set","p":"start","pt":"msg","to":"mqtt_topic","tot":"env"},{"t":"set","p":"end","pt":"msg","to":"mqtt_end","tot":"env"}],"action":"","property":"","from":"","to":"","reg":false,"x":280,"y":60,"wires":[["261b55b08d58dc2a"]]},{"id":"261b55b08d58dc2a","type":"template","z":"aa026e7dddedecc7","name":"","field":"topic","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"{{{start}}}{{{end}}}","output":"str","x":460,"y":60,"wires":[["2b7f30fc05ca40a2","0007781504e401b1"]]},{"id":"0007781504e401b1","type":"debug","z":"aa026e7dddedecc7","name":"debug 2466","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":410,"y":200,"wires":[]},{"id":"e8ba3ef5.22f4a8","type":"mqtt-broker","name":"testb","broker":"192.168.1.25","port":"1883","clientid":"","autoConnect":true,"usetls":false,"compatmode":false,"protocolVersion":"4","keepalive":"60","cleansession":true,"birthTopic":"","birthQos":"0","birthRetain":"false","birthPayload":"","birthMsg":{},"closeTopic":"","closeQos":"0","closePayload":"","closeMsg":{},"willTopic":"","willQos":"0","willPayload":"","willMsg":{},"userProps":"","sessionExpiry":""},{"id":"6bfb6de15b27e2c1","type":"subflow:aa026e7dddedecc7","z":"d1395164b4eec73e","name":"","x":460,"y":3480,"wires":[]},{"id":"508728d4a9148935","type":"mqtt in","z":"d1395164b4eec73e","name":"","topic":"MicrodesysRed/f/test","qos":"2","datatype":"auto-detect","broker":"e8ba3ef5.22f4a8","nl":false,"rap":true,"rh":0,"inputs":0,"x":260,"y":3560,"wires":[["d3e3a8c179685bc6"]]},{"id":"d3e3a8c179685bc6","type":"debug","z":"d1395164b4eec73e","name":"debug 2465","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":470,"y":3560,"wires":[]},{"id":"51a2de387bd8320c","type":"inject","z":"d1395164b4eec73e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":240,"y":3480,"wires":[["6bfb6de15b27e2c1"]]}]

There are other ways but this is using low code option.

[domingopdf]

What you gave me works great, thank you very much for the quick response, however, I don't want the second part to be a variable, I need it to be a text.

Thanks!

[E1cid]

Then delete {{{end}}} and add the text you require
{{{start}}}anytextyouwish

You could drop the change node to, as the template uses env vars( i forgot)
{{{env.mqtt_topic}}}anytextyouwish