What is the difference between $(command) and `command` in shell programming?

Question

To store the output of a command as a variable in sh/ksh/bash, you can do either

var=$(command)

or

var=`command`
         


        

Answer 1

"What's the difference if any between the two methods?"

Make attention to this behaviour:

A="A_VARIABLE"
echo "$(echo "\$A")"
echo "`echo "\$A"`"

You will get these results:

$A
A_VARIABLE