The Lazy Typist's Guide to Shell History Expansion

If you've spent any time in a terminal, you've probably typed a command, hit enter, watched it fail with "Permission denied," and then sighed as you retyped the whole thing with sudo stuck on the front. There's a better way, and it's been sitting in your shell this whole time.

The Classic: sudo !!

!! is bash and zsh's shorthand for "the last command I ran." Prefix it with sudo, and your shell expands it into the previous command with elevated privileges:

$ apt update
Reading package lists... Done
E: Could not open lock file /var/lib/dpkg/lock-frontend - Permission denied

$ sudo !!
sudo apt update

Most shells will echo the expanded command before running it, so there's no mystery about what's actually executing. It's a small trick, but once it's muscle memory, retyping a failed command feels almost old-fashioned.

The catch: !! re-runs the command exactly as you typed it, typos included. If you fat-fingered a flag or misspelled a package name, sudo !! will happily repeat the mistake with more permissions.

It Doesn't Stop at sudo

!! is just one piece of a much larger event-designator system that bash and zsh inherited from the original C shell. A few of the more useful ones:

• !$ — the last argument of the previous command. Handy when you mkdir some/long/nested/path and immediately want to cd !$ into it.
• !^ — the first argument of the previous command.
• !* — all arguments of the previous command, useful for reusing a whole file list.
• !n — re-run command number n from your history (check history for the number).
• !string — re-run the most recent command starting with string. !git reruns your last git-something.
• !?string? — re-run the most recent command containing string anywhere.
• ^old^new — quick substitution: reruns the previous command with old replaced by new. Great for fixing a single typo without retyping everything.

A quick example combining a couple of these:

$ touch report_final_v2.md
$ mv !$ report.md
mv report_final_v2.md report.md

The zsh Extras

zsh supports all of the !-expansions above natively — they're a Bourne/C-shell holdover, not bash-specific. But zsh also layers on its own history search that's worth knowing:

• Type a few characters and press Ctrl+R for reverse incremental search, same as bash.
• Type the start of a command and press the Up arrow — with the standard history bindings, this searches history for lines starting with what you've typed, not just cycling chronologically.
• The sudo Oh My Zsh plugin (if enabled) binds Esc twice to prepend sudo to the current line — a nice complement to sudo !!, since it works even before you've run the command.

Why Bother

None of this is essential — you can always arrow-up and edit, or just retype. But history expansion shaves down the friction of the "run, fail, fix, rerun" loop that makes up a surprising share of a terminal session.

sudo !! is the gateway drug. !$, !*, and ^old^new are where it starts actually changing how you work.