Do you spend most of your time in the terminal, or are you trying to learn? Bash is very mature, and it packs a lot of hidden features. Today, I have seven command-line tricks that will save you time typing and editing.
Most of these tricks leverage Bash’s history expansion. You’re probably familiar with its most basic syntax—!!—which re-executes the previous command, but there’s more to the story here, and history expansion goes a bit deeper. We can use expansions to select a command, modify it, and then re-execute.
Bash’s history expansions comprise three segments, and what you saw (“!!”) constitutes the first segment, called the event designator. There are two more segments called the “word designator” and (optional) “modifier.” We put them together like this:
event-designator[:word-designator[:modifiers]]
A real-world example is easier to read:
!!:2:p # You can use multiple modifiers, like :p:h.
- Event designator (e.g., the second “!” in “!!”): Defines which command in your history to target.
- Word designator (e.g., “2”): Defines which words (command arguments) to target. Words are generally separated by spaces or surrounded by quotes. Word zero is the command name.
- Modifier (e.g., “p”): Optionally defines what to do with the chosen word.
Broadly speaking, select a command, specify a word, and then optionally modify it. “!!:2:p” selects the previous command (“!!”), the second argument (“2”), and prints it (“p”.)
The first “!” activates Bash’s history expansion, and the expression that follows (e.g., another “!”) is the event designator. This value dictates which command you select. The only exception to a “!” prefix is “^,” which activates a string replacement (covered later.)
Operating System
Ubuntu Linux 22.04 LTS
CPU
13th Gen Intel Core i7-1360P
GPU
Intel Iris Xe Graphics
RAM
16GB DDR5
The official documentation provides lists that describe all the possible combinations. It’s challenging to see the value to begin with, but once you find a few useful tricks and understand how to form them, you’ll intuitively use them without thinking. Below, I have a few tricks I’ve found useful over the years.
Reuse all arguments
Different commands can sometimes use the same arguments
Credit: Lucas Gouveia/How-To Geek
There are scenarios where you need to apply identical arguments to multiple commands. Take the following example:
touch foo bar
chmod 644 foo bar
It would be nice if we could reuse the arguments—”foo” and “bar”—and we can:
touch foo bar
chmod 644 !!:*
It says, “Select the previous command (“!!”) and reuse all its arguments (“*”). It’s the same as executing chmod 644 foo bar.
However, Bash allows us to shorten it even further by omitting a “!:” for symbol-based word designators (“*”, “^”, “$”, and “%”). For example:
touch foo bar
chmod 644 !*
“!*” is the same as “!!:*.”
Reuse the nth argument
Some arguments are too difficult to retype
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Similar to the previous expansion, we can select specific arguments from a command:
touch foo bar
chmod 644 !!:2 # Select the second word of the previous command.
It’s the same as:
chmod 644 bar
To elaborate on event designators a little, let’s choose a different command:
The event designator (e.g., the second “!” in “!!”) is how we choose a command.
touch foo bar
ls
chmod 644 !-2:2 # Select the command two places behind (“-2”), and choose the second (“2”) word (“bar”).
“!” activates history expansion, and “-2” chooses the command two places behind in your history. In comparison, “!!” is shorthand for “!-1” (previous command).
Event designators are flexible, and you’ve probably used them before when re-executing a command from your history, e.g., !100.
Reuse the command name
It’s useful once committed to the brainstem
Credit: Lucas Gouveia/How-To Geek
Typing out the command name is easy, so you may wonder if this trick is worth the effort. Well, typing out “!:0” is even easier, and once you’ve built a habit of doing so, you do it without thinking (like !!):
touch foo bar
!:0 baz
This is the same as touch baz.
- “!”: Activates history expansion.
- “0”: Select only the command name.
Excluding the event designator (the character after the first “!”) implies the previous command.
You can select any command by specifying a number as the event designator:
!100:0 baz
However, in that case, it’s probably easier to type the command instead.
Fix a typo
Because manually replacing mistakes is a pain
Credit:
Lucas Gouveia/How-To Geek
It would be silly of me to ask if you’ve ever mistyped a command—of course you have. However, you’ve probably strained your fingers and mental energy fixing them—struggling to move the cursor to the correct place and amending the commands. There is an easier solution: a string replacement.
ehco foo bar
^ehco^echo
It’s a simple string replacement, and you can change any part of the command:
echo “Any part of the cmd.”
^cmd^command
If you’re familiar with sed, the previous expansion is the same as the following:
echo “Any part of the cmd.”
!!:s/cmd/command/
Reuse the first or last argument
It’s more convenient than specifying argument numbers
Credit: Lucas Gouveia/How-To Geek
We’ve seen how to reuse all arguments from a history entry (e.g., “!*”), but we can specifically pick the first or last argument.
Pick the first argument:
touch foo bar
chmod 644 !^
That’s the same as executing chmod 644 foo, and “!^” is equivalent to !!:1 (previous command; first argument.)
Pick the last argument:
touch foo bar
chmod 644 !$
That’s the same as chmod 644 bar.
“$” is particularly useful if you don’t know the number of arguments.
If you know regex, you’ll be familiar with “^” and “$” already, which mean the start and end of a line. That’s a handy way to memorize them.
Expand before submission
Check the command before executing it
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All of these expansions can be a little confusing unless you ground them by viewing real (expanded) commands—that way, you can see what they actually do.
To do that, type out your expansion and hit Ctrl+Alt+E:
touch foo bar
chmod 644 !$
That will expand the expression into literal values without executing the command. Now you can see what it does before executing it.
Move to the start or end of the command line
Moving around is difficult, and shortcuts make it easy
Credit: Lucas Gouveia/How-To Geek
Moving around the command line isn’t obvious to beginners, but Bash provides several shortcuts to assist you. Two of them will move you to the start or end of the line, with Ctrl+A or Ctrl+E, respectively.
Alternatively, if you know Vim, you can enable vi mode by putting the following in your .bashrc file:
set -o vi
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That’s all I’ve got today. Remember to check out the official documentation for history expansion, because it has lists that describe each segment, and you can easily squeeze a lot more out of these tips.
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