Making commands in linux

How to create my own command in linux

I wrote a simple cpp code by using vi. I want to use cat command inside this program (by using execl and it will take my file as argument). I also have to write my own command. For example it will work like that: $mycommand filename. And cat command which is inside my cpp code will show my cpp file’s content. I’m new so I don’t know how to do it. Do you have any suggestions?

1 Answer 1

1) Redirecting output
The output of the cat command should go to the standard output of your program. For this your program should pass its standard output FD to the exec command. This will be the default case. So you don’t have to do anything extra.

2) cat on the source file
Now, the cat thing : «And cat command which is inside my cpp code will show my cpp file’s content. » This statement does not explain your need. If you want the cat of the executable you are running, you can do an objdump on your executable. The executable path can be found out from the proc file system with your pid. For a generic case, it does not matter whether the file is a cpp file or not.

3) making command
To make your executable run as a standard command on a terminal, you must add the directory containing the executable to the PATH directories list. You can do so by adding your executable to /usr/local/bin or /usr/bin. (Convention is that it should go in /usr/local/bin since it has been compiled locally). If you don’t have administrator privileges on the machine, you must append the source directory to the PATH directory list.

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How to Create Your Own Commands in Linux

Arunachalam B

In this article, let’s learn about creating your own commands in Linux. Yes – we’re going to talk about creating an alias command.

Before we begin, I want to tell you how the idea for this tutorial came about.

One of the followers of my blog asked me,

«Hey Arun! I wonder about your brain’s capability to store a lot of commands. How is that possible?»

«I’ve been learning Linux and writing code since I started college (almost 7+ years). During that time I encountered a lot of errors and solved each and everyone on my own which helped me to master it», I replied.

«Even then, how could you memorize those flags and options along with each command?», he enquired.

«I cannot memorize each and every command with its options and flags. So, I create my own commands», I replied.

«What? You created your own commands? Can I create my own commands?», he asked with great excitement.

«Yes. You can. It’s called an alias command in Linux», I replied.

He asked me to write a blog on it and here it is. Let’s learn about alias commands in this blog.

What are Alias commands in Linux?

The alias command provides a string value that replaces a command name when it is encountered.

The alias command lets you create shortcuts for long commands, making them easier to remember and use. It will have the same functionality as if the whole command is run.

How to Create Your Own Linux Commands

Using the alias command, you’ll be able to create your own commands. It’s so simple to create your own command.

Here’s the syntax for the alias command:

Let’s create our command called cdv to navigate to the Videos directory. To achieve that, you have to enter the following command in your terminal:

We have created our command. From the above screenshot, you can see that it does not return anything.

But, how can we verify that the command is created and it is working?

There’s only one way to verify if the command is working: that’s by executing the created command.

Run the cdv command on your terminal to see what happens:

BOOM. You created your own command.

How to View Created Alias Commands

You may have the following question after creating a few commands:

Let’s assume I created multiple alias commands. How can I view all of them together? How can I view the equivalent command of my alias?

You can view all your alias commands by appending the -p flag to the alias command like this:

I have created many alias commands. From the above screenshot, you can see all the alias commands that I’ve created.

How to Remove an Alias Command in Linux

Pass your alias name to the unalias command as an argument to remove the alias command.

How to Remove All Alias Commands in Linux

Let’s assume you have added around 20 alias commands. After some time, you realized that using alias commands will make you forget other commands in the long term. Fearing that, you wish to remove all the alias commands.

We have a command to achieve that:

You may be curious to know more about one thing that I’ve written in the above passage.

«After some time, you realized that using alias commands will make you forget other commands in the long term»

Is this something you should worry about? Can this happen?

The answer to your first question is, yes. Definitely, you’ll get this feeling when you’re learning and trying out alias commands. Because I had the same feeling.

The answer to your second question is, absolutely no. This will result in increased productivity. There’s a high chance that you’ll forget the command you created but you’ll never forget the original command. So I always recommend revisiting your alias commands often and ensure you’re using all the alias commands you created.

I have a shocking surprise for you. Open a terminal window and create an alias command (we’ll use the cdv command we created above). Open another terminal window and type the cdv command there.

Yes. If you create an alias command, it’ll be active only for the particular instance of the terminal. It’ll not be created permanently, so you won’t be able to access it in two different terminal windows unless you run the alias command on both terminals.

How to Create a Permanent Alias Command

To create a permanent alias command, you have to add the alias command to the shell configuration file. There are many shell configurations available. A few of the well-known shells are:

Most Linux distros work with bash , so let’s look at creating a permanent alias in the bash shell. Other shells work pretty much the same.

Let’s open the .bashrc file using Vim.

You may open multiple windows and check by entering the alias -p command.

Some Helpful Alias Commands to Try

Here’s a bonus for you all.

At the company where I work, we follow common alias commands, which we set up in everyone’s machine at on-boarding. If people wish to add their own commands, they’ll be able to do so and it’ll not be reflected for others (built with the OCP principle in mind). We feel highly productive in using those commands.

I’ve planned to share a part of those commands with you all.

You can either follow the instructions in the README file of this repo or follow the instructions below to set up the alias commands on your machine.

Navigate to the Home folder

You’ve installed it the right way if you get the above message.

Let me explain the alias commands you’ll have access to using this repo.

Alias Command	Original Command	Description
f	cd $1	Go forward. Navigate to the next specified directory
b	cd ..	Go backward. Navigate back 1 directory
c	code ./	Open Visual Studio Code in the current directory
e	exit	Close the terminal tab/window
home	cd ~	Navigate to the home directory
a	xdotool key ctrl+shift+t	Open a new terminal tab
cdb	cd —	Go to the last directory where you were previously
gst	git status	Find the status of the git repo
gpr	git pull -r	Pull and rebase the git commits
glo	git log —oneline	Show git commit logs in a single simplified line
gcl	git config -l	Show the git configuration of the current repo
gca	git commit —amend	Add the current changes to the existing commit
gcane	git commit —amend —no-edit	Add the current changes to the existing commit without editing the existing commit message
ad	~/Android/Sdk/emulator/emulator -list-avds	Show available android emulators
off	sudo /opt/lampp/lampp stop poweroff systemctl poweroff -i	Turn off your machine
bb	if [ -z «$1» ] then b;b else for (( i=0;i<$1;i++ )) do b done fi	It’s an advanced version of go back command. Entering the b command goes back to only one directory. But entering bb goes back to 2 directories. If you want to go 5 directories back, run bb 5 command
pokill	kill $(lsof -t -i:$1)	Kill the program running on the port
cc	sudo nano ~/x-commands/aliasCommands.sh	Edit the alias commands file
bc	sudo nano ~/.bashrc	Edit the .bashrc file
scc	source ~/x-commands/aliasCommands.sh	Refresh the terminal after updating an alias command
bcc	source ~/.bashrc	Refresh the terminal after updating .bashrc file
welcome	echo Welcome to shell automation echo Enter Your Name read testName echo Welcome to new shortcut world ~~ $testName ~~ Enjoy Coding.	Verify if alias commands installation is done right

If you look at the aliasCommands.sh file carefully, you’ll see that I’ve added a few functions. You may wonder why I use functions. Read more to have a quick dive into this topic.

How to Run Multiple Commands in a Single Alias Command

You can achieve this in 2 ways. Let me explain both of them here.

Let’s learn this with an example.

Say you have to create an alias command called gohome . Running this command should take you to the home directory and display the «Navigated to home directory» message.

Method #1:

This way is the usual way of adding an alias command. You have to add the two commands separated by a semicolon ( ; ).

Method #2

This is a bit of a different way. To achieve this you have to make a change in your .bashrc file. You have to define a function in the .bashrc file with all the commands nested within it.

Open the .bashrc file using Vim.

Note: Creating a function will not list it as an alias command on running the alias -p command.

Conclusion

In this article, you learned how to create your own commands in Linux.

Using an alias command will definitely increase your productivity. I’ve witnessed exponential growth in many people after seeing them using alias commands. I would recommend that you all setup your own alias commands.

To learn more about Linux, subscribe to my email newsletter on my site and follow me on social media.

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