Advanced CLI: Commands You Should Know as a Developer
No, in this article we won’t go over the basic commands like
cd. You shouldn’t be shocked by seeing those commands. You might even be quite familiar with them. Especially if you know your way around the command line pretty well. I assume you have at least worked (or tried to work) on the command line before. If you’ve never worked on the command line before, I suggest you start by reading about the basics.
This article is for those of you who have some experience with the command line and got a taste of the basic commands. For those who feel like it’s time to dive deeper into the possibilities of working with the command line. I’ve listed six commands for you in this article and included some tips at the bottom as well.
On Unix-like operating systems, the
wget command downloads files served with HTTP, HTTPS, or FTP over a network. By default, it is included in all self-respecting Linux distributions.
The most simple way to use
wget is to provide it with the location of a file to download over HTTP. Downloading the file
wget can be done by the following command:
One great thing about wget is that it’s non-interactive, which means that it can run in the background while the user is not logged on. This allows you to start a retrieval and disconnect from the system, letting
wget finish the work.
Ever had a problem where you needed to have a file from a remote server on your local machine? Getting a file that a user uploaded that caused some trouble, for example.
You could download this file via the command line using the
scp command. Scp is short for secure copy. But what’s even more important is that it’s a remote secure copy. This command is similar to the
cp command that you probably already know, but either the source or the target is on another system.
The following command copies the file
foobar.txt from a remote server to a local directory.
scp firstname.lastname@example.org:/path/to/foobar.txt /some/local/directory
scp can also be used to copy a file from a local directory to a remote server.
scp /some/local/directory/foobar.txt email@example.com:/destination/path/
The same can be done with directories using the
-r option, which copies entire directories recursively.
ssh-keygen command is used to generate a new SSH key pair. The public SSH key that is generated by this command can be used in Gitlab or Bitbucket to establish a secure connection.
Once you’ve added your SSH key to either Gitlab or Bitbucket, you won’t be prompted for a password every time you try to push your files to a remote branch.
To generate an SSH key pair, use the following command:
ssh-keygen -t ed25519
Note that in the example above, we used the ED25519 signing algorithm. While ED25519 is considered best practice, you should always do some research on the different available signing algorithms.
Generating the SSH key pair and setting it up correctly in Gitlab or Bitbucket costs you ten minutes at a maximum (probably more like three) but will be totally worth it!
In Unix and Unix-like operating systems, chmod is the command and system call which is used to change the access permissions of file system objects (files and directories).
According to Wikipedia, this is the definition of the
chmod command. We’ve all been in a situation where a server didn’t have access to a certain file because of a misconfiguration in the file permissions.
chmod command is fairly simple in itself, but giving the right permissions to files and directories is a whole different game.
chmod 664 robots.txt
chmod 775 public/images
The first example gives read and write permission to user and group for the
robots.txt file. Read permission is granted to others for this file.
The second example gives read, write and execute permission to user and group for the
public/images folder. Others are granted read and execute permission for this folder.
If you want to know more about setting the right permissions to files and directories, I suggest you read the Wikipedia page about
tar stands for tape archive. It is used for collecting many files into one archive file.
Tar is the most widely used command to create compressed archive files.
Let’s start with how you can create an archive file for a specific directory:
tar -cvf my-archive.tar /path/to/directory
This command will result in an archive file, called
my-archive.tar, that contains all files of the
/path/to/directory which is created in the current working directory.
Creating the archive file is part one. Part two consists of untarring the archive file, because at some point we want to use the files in the tar file. You can untar the file into a specific directory by typing in the following command:
tar -xvf my-archive.tar -C /home/myfolder/
Everyone uses some commands that are a little too long or complex to completely remember. Luckily, you can create an
alias for that command so you don’t have to remember the entire command.
alias short-command="your custom and very long command here"
Though creating an alias this way comes with one problem: This alias is temporary. If you create an alias this way, it will only be available for your current terminal session.
To keep aliases between sessions, you can save them in your user’s shell configuration profile file. This profile file is probably located at either ~/.bashrc or ~/.zshrc if you’re using Bash or ZSH, respectively.
Tip 1: Directing Output
The standard output device is the screen. But sometimes you don’t want to output everything on your screen. In some cases, you probably prefer to output the results of some commands to a file. For logging purposes, for example.
To redirect the output, you can use the >. In the following command, the output of
ls -al is redirected to the file
myfile instead of the screen.
ls -al > myfile
ls in this example, but it really could be any command that has some output. To confirm that this worked, you can check the
Tip 2: Combining Commands
It’s possible to run two or more commands at once. The semicolon (;) operator allows you to do this. You can execute multiple commands in succession, regardless of whether each previous command succeeds.
ls -al; pwd;
If you want the second command to only run if the first command is successful, separate the commands with the logical AND operator, which is
mkdir images && cd images
We only want to
cd to the
images folder if we managed to create that folder.
And sometimes you might want to execute a second command only if the first command does not succeed. To do this, we use the logical OR operator, which is