| $(command) | replace with the standard output of command |
| $((arithmetic-expression) | replace with the result of arithmetic-expression |
| $(<file) | replace with the contents of file |
| `command ` | replace with the standard output of command |
| ~ | replace with $HOME |
| ~user | replace with the home directory of user |
| ~?/P> | replace with $OLDPWD (previous directory) |
| ~+ | replace with $PWD (current directory) |