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Fix Mistakes in Shell Commands Easily With `fc`

mayeu profile image Mayeu Originally published at mayeu.me on ・2 min read

From time to time, it can be quite cumbersome to fix a mistyped command in your shell. What if you could fix the command you just typed in your favourite editor? Well, that’s exactly what fc command is all about, and it is standard to all Unix system (this includes GNU/Linux & macOS). Let see how that work.

From Wikipedia:

fc is a standard program on Unix that lists, edits and reexecutes commands previously entered to an interactive shell.

Using fc looks something like this:

  1. You type a non-working/wrong command
  2. You type fc
  3. The last typed command (before fc) is open in your editor
  4. You fix the command, save, and quit
  5. When you exit the editor, the edited command is executed

Here is an interactive example in which I use the wrong path and fix it via fc (click on the image to see it in action):

asciicast

Of course this example is a little bit contrived because you should use autocompletion to navigate folders and not type your path entirely.

Checking my history, I have found this big command (which check if Homebrew’s ZSH path is part of the /etc/shells file, and if not, add it):

export zshpath="$(brew --prefix)/bin/zsh"; \
grep -q "^${zshpath}" /ec/shells || \
sudo -E sh -c "echo '$zshpath' \>\> /etc/shells"

It is not obvious, but there is a mistake right in the middle: /ec/shellsinstead of /etc/shells. With fc fixing this is really easy to fix since I will have access to my whole editor and not only my shell movement and shortcut.

But that’s not all fc can also take an argument to fix an arbitrary command from your shell history, not only the last one.

Use fc -l to list your history

$ fc -l
6213 rm -rf test
6214 brew install asciinema
6215 vim ~/bin/mac-bootstrap
6216 exit
6221 ls
6222 mkdir right-path
6228 asciinema rec
6229 cd wrong-path
6230 fc
6231 cd right-path
6232 pwd

Then you can use fc <history number> to fix a specific command:

$ fc 6214 # Will open “brew install asciinema” in your editor

There is not much more to this tool, but you can find the full documentation of fc here if want to check out the other arguments.

This post was originally published on my website: mayeu.me.

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