Bash History Expansion and Prompt Magic

Interesting and useful use cases of !, #, and ? expansions in Bash

I love to always learn new Linux shell commands and wrangling moves. This recent days I learned a few useful command line “tricks” that I’ve never seen anyone using so I thought of sharing them.

They all cover the special characters and escape sequences related to history expansion and prompt customization. This post will:

1. Clarify the real tools behind !, #, and ? in Bash.
2. Walk through practical examples you can copy and adapt.
3. Challenge assumptions by revealing lesser-known tricks.
4. Deliver actionable steps to integrate these shortcuts into your workflow.

[!INFO] Some of this “chops” are not as intuitive so I guess it’s a matter of practicing a few at a time so eventually they become second nature. I’ve found that when we’re working on the command line, we do sub-second operations that rely 100% on muscle memory and intuition, so it’s useful to learn this “tricks” before we ever need them so they’re there in our memory when we actually do.

Bash History Expansion (!)

#

Bash’s history expansion allows you to recall and re-execute commands from your session’s history.

• !! — Repeat the entire last command.

This may be the most commonly needed one: when we forgot to use sudo and need to run our command again…

$ sudo !!          # run the previous command with sudo

• !n — Execute command number n from history.

  $ history          # get list
  42  ls
  43  pwd
  44  echo hello
  $ !43              # runs `pwd`
  

• !-n — Run the command n lines back.

  $ !-2             # repeat the command two steps ago
  

• !string — Execute the most recent command starting with string.

  $ !ec             # runs `echo hello` if that was the last matching
  

• !?string? — Execute the most recent command containing string.

  $ history
  50   ls /var/log
  51   cat /var/log/syslog
  52   echo done
  $ !?syslog?          # runs `cat /var/log/syslog`
  

• Word designators — Extract portions of the previous command:

  • !:0 — The command itself (e.g. cat).
  • !:1 — First argument (e.g. /var/log/syslog).
  • !:n — nth argument.
  • !$ — Last argument (same as !: -1).
  • !^ — First argument (!:1).
  • !mkdir:$ — “Fetch” last mkdir command in our history, and “reuse” its argument (See example below)

For example, having written a command with a large argument, and wanting to reuse it with other command:

• Here, we “reuse” mkdir argument, which we don’t want to write again, and just append “README.md” to create a file there:

Since we cannot simply use !$ because mkdir is not our last command anymore, we can “fetch” it from our history and “reuse” its argument:

That’s it for this quick recap. Those new “chops” are very useful for those long work sessions on the terminal and can save us some precious time with tedious commands.