Father and son on shell shell (command: pstree)
Bash is a front parent shell, after a child is bash shell, a terminal corresponding to another open a terminal. (Not recommended to open too much, this thing is used for multi-threaded)
The special symbols :( shell) {}
The role of parentheses is to open a new Shell be executed in the current shell, but when the child runs out of the shell command sub-shell will disappear, returning to the parent shell. Braces instruction is to execute in the current Shell. Size brackets are in a string of instructions and inter-instruction to use brackets; separated. Which after the last command to add curly braces; parentheses and curly braces can not start and end to a space.
Course Note: braces format. But hardly use braces because of its role and does not increase the parentheses are always the same, normal writing instruction format may omit the cumbersome braces.