Q:

Some characters are filtered in bash

I'm currently running a Xubuntu image using VirtualBox and a strange issue just started occurring: I cannot enter a or c in a terminal or terminal emulator. A and C (that is, a/c + left/right Shift or with Caps Lock active) work just fine, and a/c work fine in graphical applications; it's only when using the full terminal or xfce4-terminal/xterm that the keys don't work. This seems to be a user-specific thing, as I can use a and c just fine when entering the user name for login at a terminal but once logged in the keys no longer work; however, I cannot figure out what settings I changed to somehow cause it.
Additional info: the characters are also filtered when pasting text into a terminal emulator; for a moment, I was able to get a to paste as part of a string when it was at the front, but I'm no longer able to.

A:

Since this problem occurs on different terminal types, and occurs at a command prompt but not when some other program is reading from the terminal, this is a configuration problem in your shell. You've accidentally defined bindings for a and c.
Assuming that your shell is bash (the default interactive shell on Ubuntu), check the two relevant configuration files in your home directory:

.inputrc, the configuration file for the readline library, which bash uses. Look for a line starting with a and a line starting with c.
.bashrc, the configuration file for bash when it runs interactively. Look for a line containing bind a… and a line containing bind c….

