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

When the older back-tick form is used, backslash retains its literal meaning except when followed by $, `, or \. The first back-tick not preceded by a backslash terminates the command substitution.

When using the newer $(command) form, all characters between the parentheses make up the command; none are treated specially.

Both forms can be nested, but the back-tick variety requires the following form.

`echo \`foo\`` 

As opposed to:

$(echo $(foo))