Fc (Unix)

fc (short for fix command¹) is a shell command that lists, edits and re-executes commands previously entered in the shell. It is particularly helpful for editing complex, multi-line commands. Originally developed for Unix and standardized by POSIX, the command is available in many operating systems today.

As it is required to be "intrinsic" by POSIX,² it is implemented as a builtin in the Bash, Zsh, and Almquist shells.

Invoked with no options, the command opens a text editor, allowing the user to modify the last-run command. Upon exiting the editor, the modified command is executed in the current shell.³ The editor used can be specified with the -e option; otherwise it is read from the FCEDIT environment variable,⁴ or, in some shells, EDITOR,⁵⁶⁷ with a fallback to vi or ed. Command-line options allow for quick substitution, repetition or modification of a specific command from the session history, or a range of commands from the history.

When invoked with the -l option, the command lists recent lines from the session history:

$ fc -l
1	 pwd
2	 whoami
3	 ls
4    ls -a

When invoked with -s PATTERN, the command re-runs the most recent command matching PATTERN:

$ fc -s ls
ls -a
.  ..  .bash_logout  .bashrc  .profile

Option -s enables inline substitution. For example, consider that the last command ls floder contains a typo. The following command runs the last command with "flod" replaced with "fold":

$ fc -s flod=fold
ls folder

It is also possible to edit and re-invoke a range of commands from the history. Often, one lists commands first like:

$ fc -l
1	 pwd
2	 whoami
3	 ls
4    ls -a
5    ls -la

Then, to run the commands identified as 1 and 2:

$ fc 1 2
pwd
/home/user
whoami
user