I found this in one of my old posts. This is the specific syntax I had to use to get my /ble/write to work properly from the linux command line. It has to do with how the linefeed character gets passed through if I recall. But I don't know if this relates at all to the problem @Grzegorz is having.
mosquitto_pub -t /ble/write/c7:6e:71:dd:ee:ff/nus/nus_tx -m $'digitalPulse(LED3, 1, 200);\n'