ROS1 Noetic Custom messages - Command line publish char[]/uint8[] support

Question

I have a custom ROS1 Test.msg message which I use in roscpp Noetic:

uint8[] a
uint8[] b

I use uint8[] to represent strings, because I can't use simple string type in my custom message and I have read that char was deprecated: "char: deprecated alias for uint8" as per https://wiki.ros.org/msg.

When I try to publish a new message of type Test with rostopic echo [TAB][TAB] autocomplete, the following appears:

rostopic pub /myTopic Test "a: !!binary ""
b: !!binary """

How can I use this !!binary "" YAML tag to input a simple string like "test" in the message contents (I can not modify the message definition).

Answer 1

You can do something like this in bash to convert a string to an uint8 array:

rostopic pub /myTopic Test \
  "a: [ \
    $(echo "Hello" | xxd -p -c 1 | xargs -I{} printf "%d\n" 0x{} | paste -sd,) \
  ]"

This will give you

---
a: [72, 101, 108, 108, 111, 10]
---