I have the following line in my .inputrc which does not appear to be working:
"\C-/": insert-comment
When I press C-/ I expect the current line to be prefixed with the comment character (#) and executed, but when I press it nothing happens.
If I change the keymapping to something like \C-t then it works fine.
Why can't I use C-/ as a keymapping?
The readline library follows the model of a physical terminal that could only transmit ASCII control characters and ANSI escape sequences. C-/ is not an ASCII control character; the ASCII control characters are c-@, C-a .. C-z, C-[, C-\, C-], C-^, C-_.
M-#? Or are they not subject to the same restrictions?
Meta-# is by convention an escape control character followed by # (or whatever character you want to "metafy"). The Readline library can also be configured to interpret the eight bit, if set, as a meta flag if the terminal (emulator) supports this. But this is very esoteric, since it restricts the input character set to seven bits.
M-/ doesn't seem to work for me either.
"\M-/" to work in .inputrc either, but "\e/": "your action here" works. In my terminal emulator combining the Alt key with almost any key prepends an Esc to the key character. You can check by pressing Ctrl-v before the Alt-key combination, this prints the output like this: ^[/ (Alt-/ used as an example).