How to find the unicode control string received by emacs for a command?

Question

I usually ssh into a machine at my university and run emacs on screen. I want to figure out what unicode strings code for a particular command ? For example when I changed the preferences in my OSX terminal app and associated the following actions to keyboard buttons then Emacs interpreted them as useful command.

Button  Action  Keystroke
end     \005    CTRL+e
home    \001    CTRL+a
pgdown  \026    CTRL+v
pgup    \033v   ESC v

I want to make more such bindings. For example if I could find out the right action for "Ctrl+_"(Undo) then I could associate that to one of the useless function keys.

So basically how can I find out what "Action" triggers a Keystroke ?

Answer 1

Two steps:

1. In any buffer, do a quoted insert of the key sequence. For example:

   C-q C-e

   Instead of calling move-end-of-line (the command that C-e is bound to by default), Emacs will insert ^E at point.

2. Hit C-b to put point on the character you just inserted, then do C-x = (bound to what-cursor-position). Emacs will print relevant information about the character at point in the minibuffer. For ^E, you'll see this:

   Char: C-e (5, #o5, #x5) point=1 of 1 (0%) column=0

   This tells you that the character code for C-e is 5 in octal, #o5 in decimal, and #x5 in hex.

Following these steps for the other key sequences you listed, it looks like "Actions" are derived from the decimal notation:

| Key Sequence | Output of C-x =               | Action |
|--------------+-------------------------------+--------|
| ^E           | Char: C-e (5, #o5, #x5)       | \005   |
| ^A           | Char: C-a (1, #o1, #x1)       | \001   |
| ^V           | Char: C-v (22, #o26, #x16)    | \026   |
| ^[           | Char: ESC (27, #o33, #x1b)    | \033   |
|--------------+-------------------------------+--------|

In short:

| Char code | Action |
|-----------+--------|
| #o5       | \005   |
| #o1       | \001   |
| #o26      | \026   |
| #o33      | \033   |
|-----------+--------|

So you'll need to follow this pattern when determining the correct "Action" for a given char code.