| COMMAND | DESCRIPTION |
| ( ) | Runs the enclosed command in a sub-shell |
| (( )) | Evaluates and assigns value to a variable and does math in a shell |
| $(( )) | Evaluates the enclosed expression |
| [ ] | Same as the test command |
| < > | Used for string comparison |
| $( ) | Command substitution |
| ‘command’ | Command substitution |