A menu file defines both the menu text and commands associated with the function key combinations. It is an ASCII text file containing instructions for the McIDAS menu system. These instructions obey certain format rules: the instructions need specific character positions. The first character in an instruction line defines the type of instruction. These characters include the following.
| Character | Instruction |
| M | Menu or Window defines the menu number described by subsequent instructions. |
| I | Initialization defines a McIDAS command sequence to run when the menu is accessed. |
| T | Text defines the screen row and column where a string of text begins, the color and the text itself. |
| F | The function key defines a McIDAS command or sequence of commands to run when a specified function key is pressed. |
| A | Alt + Function key defines a McIDAS command or sequence of commands to run when you press Alt and the specified function key simultaneously. |
| C | Ctrl + Function key defines a McIDAS command or sequence of commands to run when you press Ctrl and the specified function key. |
| S | Shift + Function key defines a McIDAS command or sequence of commands to run when you press Shift and the function key simultaneously. |
| U | User Common Pokes define values to poke into User Common whenever this menu is displayed. |
| + | + means a line is continued from the previous line (for A, C, F, I, S and T characters only). |
If the first character in an instruction line is not one of those listed above, the system treats the line as a comment line and ignores it. Each character is described in more detail below, including a character definition, format, parameter descriptions and example.