Difference between $(command) and `command` in a script

Question

What is the difference between executing a command like this:

var=$(ls -alh /dir)

And doing it like this:

var=`ls -alh /dir`

Is one method able to be used in more interpreters than the other?

Answer 1

They are both command substitution

Section 3.5.4 http://www.gnu.org/software/bash/manual/bashref.html

Bash performs the expansion by executing command and replacing the command substitution with the standard output of the command, with any trailing newlines deleted. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).

When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by ‘$’, ‘`’, or ‘\’. The first backquote not preceded by a backslash terminates the command substitution. When using the $(command) form, all characters between the parentheses make up the command; none are treated specially.

Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes.

If the substitution appears within double quotes, word splitting and filename expansion are not performed on the results.