When running a shell or most programs in a shell anything you type is echo'd back to the user's terminal by the kernel's tty subsystem. There's other special handling, too, for erase characters, Ctrl+R, Ctrl+Z, and so on.
Certain programs, (editors in particular) that run from a command line don't need or want this. For this reason they signal the kernel with an IOCTL call against the tty (terminal) device that they don't want this behaviour. They don't want special characters to do special things, either. Instead they ask the kernel for a "raw" mode. In particular, editor's like vim turn off various "echo settings". All this applies to real tty terminals on a computer's serial lines, or the virtual terminals at Alt+Ctrl+F4, or the really virtual terminals you get when you run something like gnome-terminal under a GUI.
Such programs are supposed to reset any modes they change on the virtual tty they are using before they quit, either by entering a quit editor command or by taking a signal (from Ctrl+C) for example.
If they fail to do this properly the tty is left in the funny state you have discovered. Since programs can fail to reset the terminal, the reset command was written to allow the user to recover.
I assume the interrupt is messing with the python software you are running. I'd guess that that program isn't getting a chance to reset the terminal, or is simply failing to do so.
In the vim case, when I run your example I get the same behaviour you describe. I also see a message "Vim: Warning: Input is not from a terminal" (It goes away when you reset). This is because vim isn't started normally from the shell. Instead the 'grep' and 'xargs' commands have been using the standard input, normally occupied by the tty, for purposes of passing the file names from grep tto xargs.
In your posted output from stty -a we can see "-echo", also confirming that this is the problem. If you were to kill vim in such a way that it couldn't handle the signal gracefully you would probably see the same problem.
The problem is described elsewhere at https://stackoverflow.com/questions/3852616/xargs-with-command-that-open-editor-leaves-shell-in-weird-state.
A solution for the vim case is avoid xargs and use instead:
vim $(grep foo * -l)
Here the list of files is constructed by the shell, as it had been by xargs, but the shell is calling vim, which is directly connected to the tty. There is warning message sent to the error output file, and vim sets and resets the tty settings correctly.
An alternative to reset that doesn't clear the screen is stty sane .
More references here, and another interesting one here. Another interesting solution is given in an answer to https://stackoverflow.com/questions/8228831/why-does-locate-filename-xargs-vim-cause-strange-terminal-behaviour.
Best Answer
One possibility is that the backslash key has become bound to some readline command (
readlineis the library that allows in-situ editing of shell commands, for example binding Ctrl+h to thebackward-delete-charaction).To test if that might be the case, you can try starting a bash subshell with readline editing disabled
If the backslash key works in that subshell, then the places to look for the rogue keybinding definition would be
/etc/inputrcfor the global configuration and~/.inputrcfor per-user configuration. You could also try printing out and searching the currently defined keybindings from the command line usingThe extra backslashes are required because a literal backslash will appear in the readline configuration as
\\, each of which needs a further escape in the shell. Obviously you can only do that in the subshell, if the backslash is being bound in the regular shell.FYI there is a
bindcommand option to remove a binding, but it is not clear how to input thekeyseqargument when it is already boundFor further information see
help bindin the bash command line