Harness the Combinatoric Power of Command-Line Tools and Utilities


Fixing Mistakes


Published January 28, 2019

Typos happen. Fix them with these two tricks.


Hi everyone, Brian here to talk about how to quickly fix mistakes when you typed out a command.

It happens, You make a typo and don’t realize it until after you typed the command.

One of the most common places this happens is when you’re trying to do something with sudo and you forgot to use sudo.

mkdir /var/test_dir

That command fails.

mkdir: cannot create directory ‘/var/test_dir’: Permission denied

If you type two exclamation points, !!, it’ll run your previous command again.

mkdir /var/test_dir
mkdir: cannot create directory ‘/var/test_dir’: Permission denied

But if you type

sudo !!
sudo mkdir /var/test_dir

it runs your previous command again with sudo. Not ashamed to admit I use this one all the time.

Sometimes you might just be typing too fast and you’ll make a typo in the command:

mdkir test_dir
mdkir: command not found

The command is supposed to be mkdir. I can fix that with a little bit of substitution:

mkdir test_dir

Hurray! It’s fixed! The new command prints and executes.

There you go! A couple of quick ways to fix mistakes when typing.

These approaches leverage a feature called history expansion, which you can learn more about in the book.

Thanks for watching!