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How to rostopic pub multiple line for std_msgs/String type topic

asked 2016-11-23 21:51:13 -0500

sonictl gravatar image

updated 2016-12-22 00:10:46 -0500

How to use rostopic pub to publish multiple line or \n or \r\r for std_msgs/String typed topic.

I tried as YAML commandLine said. but nothing works.

Thank you!!!

$ rostopic pub /send_BTSVR std_msgs/String ['test'] --- ['test2'] ---

Usage: rostopic pub /topic type [args...]

rostopic: error: no such option: ---

$ rostopic pub /send_BTSVR std_msgs/String ['test'] --- ['test2'] ---

Usage: rostopic pub /topic type [args...]

rostopic: error: no such option: ---

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answered 2016-12-22 03:29:04 -0500

gvdhoorn gravatar image

Not sure about the approach the wiki describes, but at least in a Bash shell, the following works for me:

$ rostopic pub /send_BTSVR std_msgs/String "data: '\
first line

second line

third line
'"

note the \ after the '. This allows you to continue on the next line.

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How is this multiple lines? There are no CR or LF in the topic that is sent. This also doesn't answer how to do \r or \n in a message

borgcons gravatar image borgcons  ( 2020-05-12 04:18:14 -0500 )edit

Testing this on my ROS Melodic/Ubuntu Bionic install I see this output:

$ rostopic echo /send_BTSVR
data: "first line\nsecond line\nthird line "
---
data: "first line\nsecond line\nthird line "
---
data: "first line\nsecond line\nthird line "

etc.

Afaict, that is a multiline string encoded in a singe std_msgs/String. A Python node subscribing to this with print(msg.data) shows me this:

$ python ./sub.py
first line
second line
third line 
---
first line
second line
third line 
---

etc.

\n==line feed==LF, which is the standard Linux newline.

\r would be something else. I've not checked how to get that in a YAML string, but I would expect it to work the same way (ie: by adding the escape sequence to the string).

Did you expect rostopic echo to also print the multi-line string?

gvdhoorn gravatar image gvdhoorn  ( 2020-05-12 07:00:02 -0500 )edit
0

answered 2016-12-22 03:03:37 -0500

rbbg gravatar image

updated 2016-12-22 03:07:17 -0500

I never got the multi-line pub to work either. The only way I figured out how to send multiline strings using rostopic pub is to make a file like this (named test.yaml):

"first line

second line

third line"

and then use rostopic pub /send_BTSVR std_msgs/String -f test.yaml

Note that there is an empty line between the lines. I am pretty sure there's an easier/better way, but I don't know it and would love to hear if anyone has an idea?

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gvdhoorn's answer seems work for me. you can have a try.

sonictl gravatar image sonictl  ( 2016-12-22 20:51:36 -0500 )edit

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Asked: 2016-11-23 21:51:13 -0500

Seen: 6,453 times

Last updated: Dec 22 '16