questions on XML/<param>tag
Here is the link to the tutorial about XML/param, I cannot figure out the meaning of the first sentence of the 3 options listed below, respectively.
http://wiki.ros.org/roslaunch/XML/param
1 textfile="$(find pkg-name)/path/file.txt"(optional)
The contents of the file will be read and stored as a string. The file must be locally accessible, though it is strongly recommended that you use the package-relative $(find)/file.txt syntax to specify the location.
2 binfile="$(find pkg-name)/path/file"(optional) The contents of the file will be read and stored as a base64-encoded XML-RPC binary object. The file must be locally accessible, though it is strongly recommended that you use the package-relative $(find)/file.txt syntax to specify the location.
3 command="$(find pkg-name)/exe '$(find pkg-name)/arg.txt'"(optional)
The output of the command will be read and stored as a string. It is strongly recommended that you use the package-relative $(find)/file.txt syntax to specify file arguments. You should also quote file arguments using single quotes due to XML escaping requirements.
