Get timestamp during roslaunch

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Bumping this with a valid reason: I have been able to find the equivalent $(eval expression) that produces a formatted timestamp and does not require any shell command hack. This also makes it work as part of arg tags, not just param tags.

<!-- Gets current time at launch execution as a formatted string -->
<arg name="time_now" default="$(eval eval ('_' + '_import_' + '_(\'datetime\')').datetime.now().strftime('%Y-%m-%d-%H-%M-%S'))"/>

Will give credit to this blog post, as it solved the missing link which I was struggling to understand: https://alspitz.github.io/blog/roslau...

According to them, by default there is no way to use python import statements inside the ROS eval substitution, unless you cheese it by manually forming the __import__('package') string. Then all you have to do is construct a valid one-liner command that produces the desired output, and you can test that by running the default python or python3 interpreter in a terminal.

Hope this helps for future reference (and to save lots of headaches)!

To do it directly inside the command in the param tag, you can use this:

<param name="start_time" command="bash -c 'printf &quot;${ROS_WORKSPACE}/%(%d-%m-%Y_%Ih%Mm%S)T.mp3&quot;'" />

The printf won't introduce the annoying \n at the end of the parameters. However, you can not directly use printf because when called inside the roslaunch, it calls the /usr/bin/printf which does not accept the % formatting. Hence, the use of bash -c.

It's possible I'm not forming the value of command correctly, but the hacky solution I found is to create a shell script that does a rosparam set and generates some stdout to put into a dummy variable.

foo/scripts/timestamp.sh:

#!/bin/sh
rosparam set dst $ROS_WORKSPACE/`date +%d-%m-%Y_%Ih%Mm%S`.mp3
echo "blah"

And the launch file:

<param name="dummy" command="$(find foo)/scripts/timestamp.sh"/>

rosparam get dst gets a timestamped filename with the mp3 suffix, and no single quotes or carriage return as mentioned in my comments to the other answer.

There will be the dummy variable hanging around:

$ rosparam get dummy
'blah

  '

The point is to make sure the script gets run before any nodes are launched that will depend on the param being set, where just running the timestamp.sh from a roslaunch <node> may or may not create the param first ( http://answers.ros.org/question/33772... ). The documentation in http://wiki.ros.org/roslaunch/XML/param isn't explicit about that but I assume it does always run the command first.

Nested roslaunches with param command?

Could that (somewhat ugly) approach also could generalize to running entire other roslaunches that would have to run then exit before the higher level launch would launch any nodes?

<!-- launch some stuff before doing anything else here -->
<param name="dummy" command="roslaunch bar xyz.launch"/>

If that works it would be an answer to some other questions here.

It produces an error:

run_id on parameter server does not match declared run_id: 9d505b9e-3991-11e7-b59e-
d8fc93bc28de vs 9d224222-3991-11e7-b59e-d8fc93bc28de

Though at the same time I can see parameters set by xyz.launch were actually set.