Command line: rostopic pub - why is required specify a topic type?

edit

I'm unsure why i must specify a rostopic type, while invoke a rostopic pub command.

rostopic pub /topic type [args...]

I think, that a message type can be deduced by internal call a rostopic info on a rostopic name.

So, after all you can improve your rosbash file to deduct the topic type

# rosbash
778 pub)
779         if [[ $COMP_CWORD == 2 ]]; then
780                 opts=`rostopic list 2> /dev/null`
781                 COMPREPLY=($(compgen -W "$opts" -- ${arg}))
782         elif [[ $COMP_CWORD == 3 ]]; then
783                 opts=`_msg_opts ${COMP_WORDS[$COMP_CWORD]}`
784                 COMPREPLY=($(compgen -W "$opts" -- ${arg}))

changing the line 783 to:

opts=`rostopic info ${COMP_WORDS[$COMP_CWORD-1]} | head -n 1 | awk '{print $2}'`

or after mig advice:

opts=`rostopic info ${COMP_WORDS[$COMP_CWORD-1]} 2> /dev/null | head -n 1 | awk '{print $2}'`
if [ -z $opts ]; then
    opts=`_msg_opts ${COMP_WORDS[$COMP_CWORD]}`
fi

Please correct my misunderstanding about a rostopic pub.