Linux Console Caps/Escape Swap

Full-fledged Linux desktop environments like GNOME or Ubuntu's Unity often have built-in keyboard mapping tools to meet user needs. At a lower level, xmodmap can be used to directly modify the X11 server's keyboard mapping. However, when working directly in the Linux console, things are a little more complicated without a display server.

My particular need is to swap the Caps Lock and Escape keys; as a vim user, I use Escape constantly to return to Normal mode. To be more efficient and avoid the possibility of repetitive strain injury from long-term pinky stretching to reach Escape, the following line can be added to the file /etc/rc.local, before the final line exit 0.

/usr/bin/dumpkeys | /bin/sed 's/CtrlL_Lock/Escape/' | /usr/bin/loadkeys

If you aren't familiar with Bash, a little explanation might be in order. First, note that this single-line command is actually three commands separated by the pipe character |. A detailed explanation can be found in the Advanced Bash Scripting Guide's chapter on I/O Redirection, but in short, piping cmd1 | cmd2 sends the output of cmd as input for cmd2.

The programs /usr/bin/dumpkeys and /usr/bin/loadkeys are fairly self-explanatory: they output keymaps for the console at the kernel level, and update that keymap if a valid file is input, respectively. The middle command, sed, is a powerful, general-purpose stream editor, and the source of much Linux wizardry. To understand what it's doing, take a look at its argument: the string '/s/CtrlL_Lock/Escape/'. This tells sed to s ubstitute the first instance of CtrlL_Lock with Escape on any matching line from its input (adding g after the last slash makes it a truly global substitution and not linewise.) The sed command then passes along the modified stream to loadkeys. Because this line is added to /etc/rc.local, it will be executed every boot, swapping Caps Lock and Escape in the Linux console.