I would like to know:
1. How is `command` used?
2. How is '$command' used?

For example, a script file that checks for apache tomcat processes that I created has the following lines:

test
set suffix=` grep "6.0.18"`
set command = `ps -ef $suffix`
echo $command //?? hoping this works...
#`command` //??

Errors when I run the file:
./test: line 4: unexpected EOF while looking for matching ``'
./test: line 5: syntax error: unexpected end of file

Can anyone help me find my mistakes?