How to replace '8' with '7' in a single step?

Question

In the Linux terminal, I initially entered the following command:

tail -n +80 numbers.txt

After realizing that I made a mistake and actually wanted to use +70 instead of +80, I wanted to correct it. To do this, I moved the cursor to the digit '8' and then entered '7', which inserted '7' before '8', resulting in '780'. To achieve '70', I needed to delete the '8'. However, this process seemed slow to me. Is there a way to directly replace the '8' with '7' in a single step, like simply replacing the '8' with '7'?

Answer 1

In Bash, if you have history expansion enabled (which is on by default though some disable it), then entering ^old^new will re-run the last command with a substitution applied (I think it's short for !:s/old/new/ or something). So in your case, ^8^7 without even having to arrow-key through the entire command.

Typing a new tail -n +70 command and pressing Alt. to insert the last argument of the previous command may be faster than editing the previous one. Similarly, tail -n +70 $_ should do the same.

(For more complex changes: Pressing Ctrlx, Ctrle will open your default editor ($VISUAL) where you can edit the command and immediately submit it.)

Answer 2

Assuming you're using bash, the overwrite mode is disabled and not bound to any shortcut by default:

Toggle overwrite mode. With an explicit positive numeric argument, switches to overwrite mode. With an explicit non-positive numeric argument, switches to insert mode. This command affects only emacs mode; vi mode does overwrite differently. Each call to readline() starts in insert mode.

In overwrite mode, characters bound to self-insert replace the text at point rather than pushing the text to the right. Characters bound to backward-delete-char replace the character before point with a space.

By default, this command is unbound.

You can add a keybinding and enable it, then disable it again once you're done, but I suppose the best thing to would be to use delete-char instead, bound to Ctrld by default:

Delete the character at point. [...]

Once your cursor is on the 8, press Ctrld to delete it, and then type in the 7.

In vi mode, when already on the 8: <Esc>r7. Or the whole thing can be done using <Esc>F8r7 (starting at the end of the line) to move the cursor to the first 8 and then replacing it with 7.