$ echo 'hello "world"'
hello "world"

$ echo "hello $0"
hello -bash
$ echo 'hello $0'
hello $0

$ echo "hello \"world\""
hello "world"

$ echo "date: `date`"
date: Fri Apr 11 10:42:21 IDT 2014

$ echo "date: $(date)"
date: Fri Apr 11 10:45:44 IDT 2014

