Chapter 4 Customizing your shell

This article is part of a self-published book project by Balthazar Rouberol and Etienne Brodu, ex-roommates, friends and colleagues, aiming at empowering the up and coming generation of developers. We currently are hard at work on it! If you are interested in the project, we invite you to join the mailing list!

Table of Contents

Shell productivity tips

I estimate that I spend around 50% of my day working in my text editor and my terminal. Any way I can get more productive in these environments has a direct and measurable impact on my daily productivity as a whole.

If you spend a good chunk of your day repeatedly hitting the left and right arrow keys to navigate in long commands or correct typos, or hitting the up or down arrow keys to navigate your command history, this chapter should help you get more done quicker. We will cover some shell features you can leverage to make your shell do more of the work for you.

On a personal level, I probably use some of these up to 30 times a day, sometimes even without thinking about it, and it gives me a real sense of ownership of my tool.

In the immortal words of Kimberly “Sweet Brown” Wilkins:

Ain't nobody got time for that.

Tab completion

When you are typing in your shell, I suggest you treat the Tab key as a superpower. Indeed, the same way your phone keyboard can autocomplete words for you, so can your shell. It can suggest completions of command names and even command arguments or options! This works by pressing Tab (twice for bash and once for zsh ).

One of the reasons zsh might be favored over bash is its more powerful auto-completion system, giving more results out-of-the-box and allowing you to navigate through the auto-completion options.

Here is an example of bash auto-completing a command name:

$ mkd < Tab> mkdep mkdir

Here is an example of bash auto-completing a command argument:

$ man mkd < Tab> mkdir mkdirat mkdtemp mkdtempat_np

And finally, an example of bash auto-completing a command option:

$ python - < Tab> - -3 -B -E -O -OO -Q -R -S -V -W -b -c -d -h -i -m -s -t -u -v -x

I suggest you get used to using auto-completion as much as possible. It can save you keystrokes, as well as make you discover command options you didn't know about.

Pro-tip: if you are using bash, you can get install the bash-completion package (using your system package-manager) in order to enable auto-completion for a wide variety of commands that do not support it out-of-the-box.

Keyboard shortcuts

The shell uses a library called readline to provide you with many keyboard shortcuts to navigate, edit, cut, paste, search, etc, in the command line. Mastering these will help to dramatically increase your efficiency, instead of copying and pasting with your mouse, and navigating the command with the ↑ and ↓ arrow keys.

The default shortcuts are inspired by the emacs terminal-based text editor. If you are already familiar with it, a lot of the default readline shortcuts might feel familiar. emacs isn't the only famous text editor in the history of computers though: another one, dating back from 1976, is vi . vi and emacs are designed in two very different ways, and have two very different logics. It is possible that one might “click” more than the other for you. If you happen to be familiar with the vi editor and are accustomed to its navigation system, you can replicate it in your shell as well by adding set -o vi in your shell configuration file. If you are using zsh with the Oh My Zsh framework that we introduced in the previous chapter, you can also use the vi-mode plugin to do this.

The advantage of using the same navigation logic and shortcuts in your text editor and your terminal is that is blurs the line between both, and brings consistency to your terminal environment. If you have no clue how emacs or vi work though, I would probably suggest you don't worry about all this for now and experiment with the default terminal shortcuts.

Navigating the current line

The following navigation shortcuts allow you to move quickly your cursor in the current command saving you from relying solely on the → and ← arrows.

Navigation Shortcut Go to beginning of line Ctrl - A Go to end of line Ctrl - E Go to next word Alt - F Go to previous word Alt - B Toggle your cursor between its current position and the beginning of line Ctrl - X - X

If you however prefer using the vi navigation system, you will first need to type Esc to switch from the Insertion mode to an emulation of vi 's normal mode, in which you can navigate in your text using the following shortcuts:

Navigation Shortcut Go to beginning of line ^ Go to end of line $ Go to next word w Go to previous word b Move to the end of the previous word e

You can go back to editing your command line by hitting the i key.

Deleting and editing text

These shortcuts allow you to quickly edit the current command more efficiently than by just using the Delete key.

Edition Shortcut Delete current character Ctrl - D Delete previous word Ctrl - W Delete next word Alt - D Edit the current command in your text editor Ctrl - X Ctrl - E Undo previous action(s) Ctrl - -

The equivalent vi -style shortcuts are:

Edition Shortcut Replace current character by another (ex: e) r - e Delete current character x Delete previous word d - b Delete next word d - w Edit the current command in your text editor v Undo previous action(s) u

Cutting and pasting

The shell provides you with shortcuts to cut and paste commands quickly without using your mouse.

Action Shortcut Cut current word before the cursor Ctrl - W Cut from cursor to end of line Ctrl - K Cut from cursor to start of line Ctrl - U Paste the cut buffer at current position Ctrl - Y

The equivalent vi -style shortcuts are:

Action Shortcut Cut current word before the cursor d - w Cut from cursor to end of line d - $ Cut from cursor to start of line d - ^ Paste the cut buffer at current position p

Controlling the terminal

Finally, these shortcuts will let you interact with the terminal itself.

Action Shortcut Equivalent command Clear the terminal screen Ctrl - L clear Close the terminal screen Ctrl - D exit Send current command to the background. Ctrl - Z

Even mastering some of these shortcuts should make you immensely more productive at typing commands and navigating command-line interfaces. I suggest you take time to experiment until you feel more accustomed with them. I can guarantee that you will feel the productivity boost!

A unified command-line editing experience

These shortcuts do not just work in your shell, but in any application using the readline library to allow the user to type and edit commands. Learning these shortcuts will thus make you productive in all types of command lines that you might encounter in your career, such as python , irb , sqlite3 , etc.

To make sure you get a smooth and homogeneous editing experience in all command lines you use in your system, you can set your preferred mode in the readline configuration file itself.

$ cat ~/.inputrc set editing-mode vi # or emacs

Navigating through history

If you find yourself typing a certain command times and times again, you should probably be aware of how to navigate and search your shell history, in order to save time and keystrokes.

While the obvious way to re-execute a previous command might seem to just bash on the ↑ key until you find the command you want, there are faster and smarter ways to accomplish this.

Searching the history

A very useful and time-saving trick is searching for a command into your shell history instead of re-typing it from scratch. You can search your command history by typing Ctrl - R which opens a reverse-i-search (backwards search) prompt, in which you can search for previously executed command containing a given search pattern.

Type Ctrl - R to navigate through the results, until you find the one you were looking for and type the Enter key to execute it.

$ < Ctrl-R> ( reverse-i-search ) : echo < Ctrl-R> < Enter> $ echo "hello world" hello world

If you want to stop the search, either hit Ctrl - C or Ctrl - G to be sent back into the regular shell prompt.

History search works by looking into the shell history file ( ~/.bash_history for bash and ~/.zsh_history for zsh by default). Every time you execute a command, it will be added to your shell history file (with a maximum number of retained commands defined by the HISTSIZE environment variable).

The location of your shell history file can be configured by setting the HISTFILE environment variable.

Rewriting history

If you want to remove a sensitive command from your history, you can simply edit your $HISTFILE history file and remove it.

$ secret-command --password 1234qwerty # oh no! that should not be in my history! $ grep secret-command $HISTFILE secret-command --password 1234qwerty $ sed -i '/secret-command/d' $HISTFILE # deletion of history line containing 'secret-command' $ grep secret-command $HISTFILE $ # it's not in history anymore

You can also use the history built-in command to display your whole history

$ history | tail -n 5 496 mkdir test 497 secret-command --password 1234qwerty 498 cd 499 man history 500 history | tail -n 5

Each history line is prefixed by its index in the history. You can then use history -d <index> to remove the associated line from history.

$ history -d 497 $ history | tail -n 7 496 mkdir test 497 cd 498 man history 499 history | tail -n 5 500 history -d 497 501 history | tail -n 7

This only works with bash , not zsh .

Avoiding history

There is a trick you can use if you want to fly under the radar and never have a command recorded in history in the first place. Simply prefix your command by a space.

If you are using zsh , you need to add setopt HIST_IGNORE_SPACE in your ~/.zshrc to make sure that behavior is enabled.

$ secret-command --password 1234qwerty # notice the space at the start of the command! $ history | tail -n 2 502 history | tail -n 7 503 history | tail -n 2

Shell expansions

The shell can perform expansions, meaning it can replace portions of the command before executing it. Relying on expansions allows you to type less and rely on the shell itself to do the heavy lifting. While there are multiple types of expansions, we will only cover 5:

history expansion: quickly access previous commands and arguments from history

tilde expansion: replace the ~ path prefix

path prefix pathname expansion: expand a path pattern into a list of files

braces expansion: expand a pattern between braces into a longer sequence

command expansion: replace a sub-command by its output

Expansions are extremely powerful. When used right, an expansion can literally save you from writing a script.

As we only over what we think are the most useful expansions and shortcuts, feel free to refer to the bash manual, section EXPANSION if you want to see the full list.

History expansion

Your shell has multiple tricks up its sleeve to allow you to quickly reference previous commands or arguments in history with a minimum of keystrokes. While this section only provides you with what we feel are the most useful of them, feel free to go to the HISTORY EXPANSION section of the bash manual.

Event designators

An Event designator is a reference to a command line entry in the history list. It allows you to quickly refer to a previous command without having to re-type it.

!-n

!-n refers to the nth latest command: !-1 refers to the latest command, !-2 to the command before that, etc.

$ echo "hello world!" hello world! $ cd $ !-2 # !-1 is "cd" and !-2 is 'echo "hello world!"' $ echo "hello world" hello world

!! is a shortcut for !-1 , aka the latest command.

$ echo "hello world!" hello world! $ !! $ echo "hello world" hello world

!! is oftentimes used in conjunction with sudo , to re-execute the previous command with superuser privileges when it failed, due to a lack of permission. $ vim /etc/myfile vim: /etc/myfile: Permission denied $ sudo !! $ sudo vim /etc/myfile

^string1^string2

^string1^string2 is used to repeat the previous command in which string1 is replaced by string2 .

$ cat ./myfile Just a file full of junk $ ^cat^rm $ rm ./myfile

I personally use and abuse of this technique when I'm about to irremediably delete some resources (files, folders, containers, etc), and I want to make sure I'm about to delete the right things by listing these resources first. If you are familiar with SQL queries, it is the equivalent of executing a SELECT query before changing the SELECT to DELETE to make sure you're not going to delete more than you wanted to.

Word designators

Word designators are used to select desired words from a previous command (by default, the latest). They can be very useful when you want to type a new command that uses arguments previously typed in a previous command.

!^

!^ maps to the first argument of your latest command.

$ touch first.txt second.txt last.txt $ vim !^ $ vim first.txt

!$

!$ maps to the last argument of your latest command.

$ touch first.txt second.txt last.txt $ vim !$ $ vim last.txt

Combining event and word designators

You can even combine event and word designators in more complex shapes by using the following syntax

[ EVENT DESIGNATOR ] : [ WORD DESIGNATOR ]

For example, you could use the !! event designator to select the last command, and the 2 word designator to select the second argument.

$ touch first.txt second.txt last.txt $ vim !!:2 $ vim second.txt

Tilde expansion

For each unquoted word starting with ~ in the command, all characters preceding a forward slash ( / ) will be considered a tilde prefix. Depending on its actual value, the tilde prefix can be expanded several ways, although the simple ~ is probably its most common use.

Tilde prefix Expansion ~ Your home directory ~+ Your current working directory ~- Your previous working directory

Example

$ ls ~ Android code Downloads Music AndroidStudioProjects Desktop Dropbox Pictures bin Documents Firefox_wallpaper.png Videos

This lists the content of your home directory, and is the equivalent to ls $HOME . You can combine the tilde with a suffix to compose an absolute path to some file or folder in your home directory.

$ cd ~/code $ pwd /home/br/code

Pathname expansion

Pathname expansions allow you to write an short path pattern and have it expanded in a list of files and directories, saving you from tedious copy-pastes or a possibly long (and error-prone) command writing.

*

The glob, or wildcard * character matches any string. It allows you to give a pattern to the shell, that it will then expand to all files and directories matching the pattern. The wildcard can be prefixed or suffixed, which will further specify our pattern. For example, *.jpg matches all files ending with the .jpg extension, and README.* matches all files named README whatever their extension.

Let us consider the following file and directory structure.

$ tree . | -- pic1.jpg | -- pic2.jpg | -- pic3.jpg | -- pic4.jpg \_ _ pics | | -- pic5.jpg | | -- pic6.jpg | \_ _ pic7.jpg \_ _ sounds \_ _sound1.mp3 2 directory, 8 files

We want to move all jpg files into our pics directory. Instead of running 4 different mv commands or manually typing a long mv command, we can run just one using a pathname expansion.

$ mv *.jpg pics $ tree . \_ _ pics | | -- pic1.jpg | | -- pic2.jpg | | -- pic3.jpg | | -- pic4.jpg | | -- pic5.jpg | | -- pic6.jpg | \_ _ pic7.jpg \_ _ sounds \_ _sound1.mp3 2 directory, 8 files

*.jpg was expanded to all files ending with .jpg , causing the shell to actually run mv pic1.jpg pic2.jpg pic3.jpg pic4.jpg pics , causing all 4 jpg files to be moved to the pics directory in a single command.

We could have executed the following command for the same result: mv pic*.jpg pics . This would have moved all files with name starting by pic and ending with .jpg to the pics directory

You can use * several times within the same pattern. For example ls */* will list all files and directories located in a subdirectory.

$ ls */* sounds/sound1.mp3 pics/pic2.jpg pics/pic4.jpg pics/pic6.jpg pics/pic1.jpg pics/pic3.jpg pics/pic5.jpg pics/pic7.jpg

Like in our second example, we can also use */*.jpg to list all jpg files located in a subdirectory.

$ ls */*.jpg pics/pic1.jpg pics/pic3.jpg pics/pic5.jpg pics/pic7.jpg pics/pic2.jpg pics/pic4.jpg pics/pic6.jpg

**

** is expanded to all files and directories in the children directories, with a depth limit of 1.

$ touch README.txt $ mkdir sounds/lyrics $ touch sounds/lyrics/sound1.txt $ tree . | -- README.txt \_ _ pics | | -- pic1.jpg | | -- pic2.jpg | | -- pic3.jpg | | -- pic4.jpg | | -- pic5.jpg | | -- pic6.jpg | \_ _ pic7.jpg \_ _ sounds \_ _ lyrics | \_ _sound1.txt \_ _sound1.mp3 3 directories, 10 files $ ls ** README.txt pics: pic1.jpg pic2.jpg pic3.jpg pic4.jpg pic5.jpg pic6.jpg pic7.jpg sounds: lyrics sounds.mp3

ls ** was expanded into ls README.txt pics/ sounds/ , which does not include the content of sounds/lyrics because of the depth limit of 1.

**/

**/ is expanded into all directories and subdirectories with a depth limit of 1 starting from our first directory.

$ tree . | -- README.txt \_ _ pics | | -- pic1.jpg | | -- pic2.jpg | | -- pic3.jpg | | -- pic4.jpg | | -- pic5.jpg | | -- pic6.jpg | \_ _ pic7.jpg \_ _ sounds \_ _ lyrics | \_ _sound1.txt \_ _sound1.mp3 3 directories, 10 files $ ls **/ pics/: pic1.jpg pic2.jpg pic3.jpg pic4.jpg pic5.jpg pic6.jpg pic7.jpg sounds/: lyrics sounds.mp3 sounds/lyrics/: sound1.txt

ls **/ was expanded into ls sounds/ sounds/lyrics pics/ . It thus listed all files located in our subdirectories.

Brace expansion

A brace expansion is a mechanism by which the shell can generate multiple strings based on a sequence of tokens defined within curly braces. The brace expansion pattern can be preceded by an optional preamble and followed by an optional postscript.

$ mkdir ~/test/ { pics,sounds,sprites } $ ls ~/test pics sounds sprites

~/test/{pics,sounds,sprites} was expanded into ~/test/pics ~/test/sounds ~/test/sprites causing the shell to execute mkdir ~/test/pics ~/test/sounds ~/test/sprites (which will be expanded further into mkdir /home/br/test/pics /home/br/test/sounds /home/br/test/sprites by a tilde expansion).

We could have done the same thing by factoring the final s of each token into a postscript.

$ mkdir ~/test/ { pic,sound,sprite } s

A brace expansion can also have a sequence pattern {x..y[..incr]} where x and y are either an integer or a single character, and incr is an optional increment value.

$ touch ~/test/sounds/noise- { 1 ..5 } .mp3 $ ls ~/test/sounds noise-1.mp3 noise-2.mp3 noise-3.mp3 noise-4.mp3 noise-5.mp3

The default increment is 1 if the sequence end is greater than its start, and -1 otherwise. However, we could specify a custom increment value if we want.

$ touch ~/test/pics/pic { 1 ..10..2 } .jpg $ ls ~/test/pics pic1.jpg pic3.jpg pic5.jpg pic7.jpg pic9.jpg

Command expansion

Your shell can replace a command surrounded by $() with its output.

I personally like use to commands expansions to iterate over a command's result, or by combining it with a heredoc redirection:

$ cat <<EOF > aboutme My name is $(whoami) and I live in $HOME EOF $ cat aboutme My name is br and I live in /home/br

Real-life examples

Moving a pattern of files contained in directories and subdirectories

What is really powerful with these expansions is that, like almost everything in the shell, they can be combined. The following example combines a pathname expansion, a brace expansion and a tilde expansion.

$ tree . | -- README.txt \_ _ pics | | -- pic1.jpg | | -- pic2.jpg | | -- pic3.jpg | | -- pic4.jpg | | -- pic5.jpg | | -- pic6.jpg | \_ _ pic7.jpg \_ _ sounds \_ _ lyrics | \_ _sound1.txt \_ _sound1.mp3 $ mv **/*. { jpg,mp3 } ~/assets/ $ tree | -- README.txt \_ _ pics \_ _ sounds \_ _ lyrics \_ _sound1.txt $ ls ~/assets pic1.jpg pic2.jpg pic3.jpg pic4.jpg pic5.jpg pic6.jpg pic7.jpg sound1.mp3

Using these expansions, we were able to move all jpg and mp3 files located in directories and subdirectories to the assets directory located in your home directory, in exactly 27 characters!

Renaming multiple directories

We could use a for loop, pathname expansion and a command expansion to rename all directories contained in the current directory to their uppercase equivalent.

$ for dir in */ ; do mv " $dir " " $( echo " $dir " | tr '[:lower:]' '[:upper:]' ) " done

Let's decompose that command into its different steps:

the */ glob pattern is expanded over the list of directories, on which we iterate via a for loop

glob pattern is expanded over the list of directories, on which we iterate via a loop we execute echo $dir | tr '[:lower:]' '[:upper:]' , which will convert the current directory name to uppercase

, which will convert the current directory name to uppercase the $(echo $dir | tr '[:lower:]' '[:upper:]') command is expanded into the uppercase directory name

command is expanded into the uppercase directory name the directory is renamed into an uppercase name

the for loop iterates over the next directory name

loop iterates over the next directory name we move on to the next directory and repeat the previous steps for each of them

Iterating over paths with a for loop is brittle as it breaks if a path contains a space. We will later see how to properly do it using the find command.

Summary

Your shell has so many productivity tricks and shortcuts up its sleeve it can be a little bit daunting. I suggest you don't try to learn them all at once, but really just experiment with them and see what feels natural. Even mastering some of them will make you more productive!

What if there is an action you find useful but you just don't like the keyboard shortcut? Luckily for you, the next chapter will dive into how to personalize and customize your shell.

Going further

5.1: Create a directory. Use a bash expansion to move into that directory without typing its name a second time.

5.2: Print your 4th last command typed into your terminal without re-typing it.

5.3: Create the following empty files README.txt , requirements.txt and TODO.txt in a single command, without typing .txt more than once.

5.4: Delete all the files created in the last question without typing .txt more than once.

5.5: Create the following directory tree in a single command.

files | -- 1 | | -- 1a | | -- 1b | | -- 1c | | -- 2a | | -- 2b | | -- 2c | | -- 3a | | -- 3b | \- - 3c | -- 2 | | -- 1a | | -- 1b | | -- 1c | | -- 2a | | -- 2b | | -- 2c | | -- 3a | | -- 3b | \- - 3c \- - 3 | -- 1a | -- 1b | -- 1c | -- 2a | -- 2b | -- 2c | -- 3a | -- 3b \- - 3c

5.6: Remove all subdirectories starting with 3 created in the previous command, while keeping the top 3 directory.

5.7: Re-execute the command from exercise 5.3 by looking backwards into your shell history.

Essential Tools and Practices for the Aspiring Software Developer is a self-published book project by Balthazar Rouberol and Etienne Brodu, ex-roommates, friends and colleagues, aiming at empowering the up and coming generation of developers. We currently are hard at work on it! The book will help you set up a productive development environment and get acquainted with tools and practices that, along with your programming languages of choice, will go a long way in helping you grow as a software developer. It will cover subjects such as mastering the terminal, configuring and getting productive in a shell, the basics of code versioning with git , SQL basics, tools such as Make , jq and regular expressions, networking basics as well as software engineering and collaboration best practices. If you are interested in the project, we invite you to join the mailing list!