bash - 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`

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

Answer 1

The backticks/gravemarks have been deprecated in favor of $() for command substitution because $() can easily nest within itself as in $(echo foo$(echo bar)). There are other differences such as how backslashes are parsed in the backtick/gravemark version, etc.

See BashFAQ/082 for several reasons to always prefer the $(...) syntax.

Also see the POSIX spec for detailed information on the various differences.