Shell Commands Every Developer Must Know
Are you still dependent on GUIs? You can significantly increase your productivity by learning a few basic shell commands. After learning these, learning more commands will come naturally — promised!
If these shell basics are well known to you, please skip this article and head to my follow-up article to become a command-line ninja!
pwd — return working directory name
Let’s start by knowing where you are once you opened your terminal:
I’m in my home directory, where are you?
ls — List directory contents
Now let’s see what is in the current directory:
AndroidStudioProjects VirtualBox VMs
There’s a lot here because I’m a messy guy, so I truncated it a little.
The ls command has many convenient options; these three I use all the time:
-l: (The lowercase letter “ell’’.) List in long format. (See below.) A total sum for all the file sizes is output on a line before the long listing
-h: used with the
-loption, this changes the file sizes into something more readable, like 10G, 42M. In my head, I translate this to ‘human-readable’
-a: Short for ‘all’; include ‘hidden’ directory entries whose names begin with a dot (.)
You can combine these any way you need, like this:
$ ls -lhatotal: 32drwxr-xr-x+ 85 erik staff 2.7K May 27 11:11 .
drwxr-xr-x 6 root admin 193B Sep 29 2019 ..
-rw-r--r-- 1 erik staff 2.1K Apr 15 11:06 .gitignore
-rw-r--r-- 1 erik staff 25M May 26 15:44 image.zip
What you see here are the access rights, the owner and group, the file size, the files last modified data, and the file name itself.
On the first two rows, you might notice something odd: two files named
.is the current directory. It even has a size, which is dependant on the number of files in the directory
..is the underlying directory, which the current directory is part of
These handy shortcuts can be used in every command. If you want to view the contents of the underlying directory, use
ls ../. You can also repeat this, so if you want to go down two directories, you can use
cd — Change directory
Now that you know where you are and what directories there are, you want to navigate around. Let’s say your projects are stored in the Projects folder. You can go there by typing:
$ cd Projects
Most shells support auto-completion. Just try it by typing:
$ cd Pro<TAB key>
Your shell will auto-complete the word or, if multiple directories match what you typed, it will usually show you all the options.
cp — Copy
You may want to copy or duplicate some files. The cp command does just that: it copies a file. It does so by creating a new file and copying all the contents to that file. To copy
file1.txt to a second file, e.g., to back it up, use:
$ cp file1.txt file1.txt.bak
To copy a file to another directory, you can use:
$ cp file1.txt ./backups/
./ means ‘the current directory,’ so ‘backups’ is located in the current working directory.
mv — Move
If you need to move a file, use the
mv command. Note that moving a file is the same as renaming a file. In fact, there is no rename command. Using
mv is not much different from
cp. To rename/move a file:
$ mv file1.txt file1.txt.bak
To move a file to another directory:
$ mv file1.txt ./backups/
mkdir — Make directories
This command will simply create a directory. To create a directory to store your projects in, use:
$ mkdir Projects
There’s one convenient argument to this command,
-p. When you use it, any intermediate directories that don’t exist yet will also be created. If you want to create your first project inside of “Projects” directly, you can do so with:
$ mkdir -p Projects/my_first_project
rmdir — Remove directories
The opposite of
rmdir, it removes a directory. It even allows the same
$ rm Projects
To remove the Projects directory and the first project we just created:
$ rmdir -p Projects/my_first_project
Removing a directory will only work when that directory is empty. If you want to remove a directory, including its contents, see the
rm command which is up next!
Now we’re getting into dangerous territory. This command is very powerful and has the potential to destroy your file system. Use it with care.
Let’s start by destroying a file:
$ rm file1.txt
Poof! It’s gone. There’s no ‘Trash Can.’
Now let’s remove all files in our projects directory that end with
.txt. You need a so-called glob pattern that matches multiple files:
$ rm Projects/*.txt
If you want to delete all files, use:
$ rm Projects/*
The glob pattern
* matches everything.
If you want to err on the side of caution, use the
-i option, which forces you to confirm the delete operation.
Now, for the grand finale, let’s delete an entire tree of directories and files. For this, you need the argument -r, short for recursive.
rm -r will sometimes refuse to remove special files, or constantly ask for confirmation. You can use the force option
-f to remove everything it can; no questions asked. Let’s remove all our projects:
$ rm -rf Projects
Poof! All your work — gone forever. Like I said, handle with care!
cat, less, tail, head — View the contents
You often want to quickly inspect the contents of a file. There are several ways to do this. Pick one that matches your use case:
cat— print everything on your screen
less— allows you to scroll through the file and even search inside it
cat, but only print the last 10 lines (by default)
cat, but only shows the first 10 lines (by default)
head take the
-n <num>option, to change the number of lines it shows.
control+r — Find your previous command
It’s easy to forget, so wouldn’t it be nice to find that command you used yesterday or last week quickly? Well, you can! Just hit control+r on your keyboard and start typing the part of the command you do remember — this can be any part!
If what you found is not entirely what you were looking for, keep searching by repeatedly hitting control+r. It will keep giving you matches from your command history.
You just learned the basic commands that help you navigate the shell. If this introduction whetted your appetite, I encourage you to keep learning and read my follow-up article called “This Will Make You a Command-Line Ninja.”
Thank you for reading. If you believe I missed something, please leave a comment!