The Linux command line and other software based on readline library support vi editing mode. After I worked on a new system with the default settings for a while, I noticed that I miss this mode very much.
It took some time to remember how I setup it on the main system. Grepping files for the line "set -o vi" has given nothing. Finally, I found that the solution is very nice and probably not described anywhere.
The file "/etc/inputrc" should contain the line:
Now, initially, the input works as usual. But when I press the button ESC, the input switches to the vi mode.