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Send A Message To Another Logged In User

Today’s article might be useful for system administrators or just for fun, as we learn to send a message to another logged-in user (in the terminal, of course). This shouldn’t be a complicated or lengthy article, though many of my recent articles have been significantly longer than usual.

If you’re just a regular desktop user, this might not be all that interesting, but you can still test it if you want. Besides, you never know when you will want to send a message to another logged-in user! It could happen.

Let’s say you have a server with people logged in via SSH. This could also be a single computer with multiple people logged in, should you wish to test this and play around with sending a message to another logged-in user. Let’s also say that you want to send them a message in the terminal.

Perhaps you’re going to log them off? Maybe you’re going to reboot the server? Who knows, maybe you want to give them some sort of directions and the easiest way to do so is to send them a message that pops up in their terminal. You can do that!

We’ll be using a few tools for this. None of them are all that complicated and these little tools (do one thing and do it well) are tools that make the Linux world go around.

For starters, we’ll be using the ‘who’ command.

who – show who is logged on

We will also be making use of the ‘awk’ command.

gawk – pattern scanning and processing language

Next, we’ll be using the ‘echo’ command.

echo – display a line of text

There will also be the ‘write’ command.

write — send a message to another user

We will also be using a pipe. We will pipe the output from one command to another command. We’ve done that lots of times on this site, so regular readers will already be familiar with a pipe and how it works.

Briefly speaking, a pipe is just one way to take the output from one command for use in another command. It’s a pretty handy tool to add to your Linux toolbox if you haven’t already done so. It’s a simple tool, which is a good thing.

If all of the above looks complicated, don’t be alarmed. It’s not all that complicated and the commands I share will be simple enough for most anyone to follow. You’ll be able to adjust them to your needs quite easily.

Send A Message To Another Logged In User:

As mentioned in the intro, you’ll want an open terminal for this. So, open your default terminal emulator. You can usually just press CTRL + ALT + T and your default terminal will open. This isn’t always true, but it’s true in many cases. You will otherwise need to open the terminal on your own.

With your terminal now open, let’s find out who is logged in. To do that, we only need the following command:

who -u

who -u

However, we only care about the first two fields, so let’s narrow that output with the following command:

who -u | awk '{print $1, $2}'

1	who -u \| awk '{print $1, $2}'

The output from that command is all we need for the next part. You use the first column to identify the username. That makes them easy to identify, or at least easier for most folks.

The other column is the 2nd one. That identifies their login method, basically which terminal they’re using, and is also what we will use to specify the recipient of our message. Next, to send a message to another logged-in user, you use a command similar to this:

echo "<message>" | write <$1> <$2>

1	echo "<message>" \| write <$1> <$2>

Or, take a look at this:

identify and send a message to a logged in user. — See? It’s not complicated. It’s harder to describe than it is to do.

So, in that case, the syntax of the command is easy, it’s just like this:

echo "this is a message" | write kgiii pts/3

1	echo "this is a message" \| write kgiii pts/3

You’ll notice that the output of the command isn’t on that screen. It was sent to the other screen, the screen where that user was logged in (specifically over SSH). It quite happily sends the message to the user logged in at that location.

You can’t use usernames alone, as it’s possible for more than one person to use the same username. This method identifies the user and the method/location they’ve used to log in. It’s a pretty handy command like that. It might look a bit complex, but it isn’t.

Closure:

So, if you’ve ever wanted to send a message to another logged-in user, you can now do that. It’s easier done than explained, but hopefully, you get the gist of it and can apply it to your personal computer usage.

It’s not always that easy to come up with ideas for articles. I often pull them from my notes, but my notes are a mess, and not all of them would make good articles. If there’s something you’d like covered, and I know the subject, feel free to contact me and let me know. Of course, don’t forget that I take guest articles when they’re about Linux.

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

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A Little About The ‘tail’ Command

Today’s article is about the ‘tail’ command, seeing as the last article was about the ‘head‘ command. The tail command is the head companion’s counterpart. It only makes sense to cover one after covering the other, so today’s article will do just that.

Like the head command, the tail command has been with us for a long time, since pretty much the earliest days of Unix. Where head shows you the first lines in a file, the tail command shows you the lines from the end of the file. The man page describes tail as:

tail – output the last part of files

The tail command is pretty handy, often used by sysadmins to monitor log files. It can also be used like the head command to quickly check the contents of a text file, but it shows the material at the end of the file and not at the start of the file. That’s useful for remembering where you left off, for example. Anyhow, there are all sorts of ways to use it and this article will explain some of them.

Getting Started With The ‘tail’ Command:

I don’t think it’s all that important for this article (I’m not sure, I haven’t written it yet!), but we can start on the same page like we did with the head command.

We’ll need to get started with the terminal open. You can do open your terminal with your keyboard – just press CTRL + ALT + T and your default terminal should open.

Once you get the terminal open, you can run the following two commands. Be sure to press the enter button after each of them and it will download a handy text file (just some random numbers) so that we’re all working on the same file.

cd Downloads 
wget https://linux-tips.us/files/rnd-num.txt

1 2	cd Downloads wget https://linux-tips.us/files/rnd-num.txt

With that complete, we can head on into the main article! It shouldn’t be all that long or difficult.

The ‘tail’ command:

Seeing as you’ve already got the rnd-num.txt file downloaded and your terminal is already open, I think we can just jump into using the tail command. If you just want to view last 10 lines of a file, you can use this command:

tail rnd-num.txt

1	tail rnd-num.txt

On the other hand, you can use the -n flag to show a specific number of lines. If you only wanted to see the bottom 5 lines, you’d use this command:

tail -n 5 rnd-num.txt

1	tail -n 5 rnd-num.txt

Assuming you’re all playing the home game, and just to show a good example, the output from the final command would look similar to this:

tail with the -n flag — As you can see, it only shows the last five lines of text. Pretty neat, huh?

Along the same lines, but not necessarily as useful, is the -c command. It works the same way it does in the head command, namely showing the specified number of bytes. If you wanted to see the final 5 bytes, the command would look like:

tail -c 5 rnd-num.txt

1	tail -c 5 rnd-num.txt

You can also use tail on more than one file at a time. If you do so, you can also use the -v flag and it will helpfully show the names of the files. The command would look a little like this:

tail -v rnd-num.txt test.txt

1	tail -v rnd-num.txt test.txt

The output would look similar to this:

tail being used on multiple files — It helpfully shows you the file names, which can be handy if you’re using multiple files.

One of the command options available with tail isn’t available with head. That flag is the -f mostly used for logs. What happens is you use the -f flag and then tail keeps running, outputting new lines to your terminal as the occur. In that case, it’d be something like:

tail -f <log>

1	tail -f <log>

That should show the last 10 lines of the log file and then update when new lines are added to the log file you’ve opened. Use man tail for more usage information.

Closure:

And that’s it! There’s another article for the site and another article closer to reaching the project’s goals. This article covers the tail command, seeing as the head command was covered in the last article. Feel free to leave a comment sharing how you use the tail command, or maybe even just a comment or question to motivate me.

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your own site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

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It’s Time To Learn A Little About The ‘head’ Command

Today’s article is about the ‘head’ command. The head command is a tool for viewing a file’s contents (or piped data), starting from the top. There’s not a whole lot to the command, and this will make be a pretty short article that’s fit for a beginner.

The head command has been with us since the heady days of Unix (See what I did there?) and is still a useful command today. In fact, the man page defines it like this:

head – output the first part of files

As you can guess, it does exactly what it says on the tin. There are any number of circumstances when you might want to use it, but I often use it when I don’t remember the exact filename I’m after and just want to see the first few lines of text as a reminder. There are better uses.

Anyhow, there’s not a whole lot to it, but I’ll show you the basics. Like we did recently, let’s see if we can all get started on the same page. So, open your terminal and enter the following:

cd Downloads
wget https://linux-tips.us/files/rnd-num.txt

1 2	cd Downloads wget https://linux-tips.us/files/rnd-num.txt

Doing that will put you in the Downloads directory and will download a text file (it’s perfectly harmless) and it means we are all working with the same settings. You do not need to do this, but it could help.

About The ‘head’ Command:

Seeing as you’ve already got the terminal open, and that you figured it out without me having to repeat it like I do in almost every article, we’ll just jump right into the first command.

head rnd-num.txt

1	head rnd-num.txt

That should output the first ten lines of the rnd-num.txt file, looking something like this:

head in action — If you used the rnd-num.txt, your output should be the same. Pretty neat, huh?

That’s the first ten lines from the rnd-num.txt file or, in other words, the head of the file has been outputted to the terminal. This has a number of uses, including the pipe. You can easily pipe it to another command. It’d look something like this:

head rnd-num.txt | cat > test.txt

1	head rnd-num.txt \| cat > test.txt

That’s not all that head can do, it can output a specified number of lines. To do that, you use the -n flag. It looks like this:

head -n 5 rnd-num.txt

1	head -n 5 rnd-num.txt

You can also use the -c flag to show the first x-number of bytes in a file. That’s not very complicated. In this case, we’ll look at the first 25 bytes.

head -c 25 rnd-num.txt

1	head -c 25 rnd-num.txt

You’ll find the output looks pretty similar to the output from the previous head command. You can even work with multiple files and the head command will handle them easily. If you’re going to use multiple files, you should use the -v flag.

head -v rnd-num.txt test.txt

1	head -v rnd-num.txt test.txt

It’ll helpfully preface the start of each file with the name of the file. In this case, the first line of the output would look like this:

head with multiple files — See? It’ll handily list the filename before listing the output.

See? Pretty helpful!

As shown in the image, you can easily deal with multiple files and whatnot, but there’s really not much more to be done with the head command. If you’re curious, you can also enter man head to get more usage information.

Closure:

Yup… There’s another article. This is about the head command, a command that’s not used often but worth having in your toolbox. If you use it more often, feel free to leave a comment explaining what you do with it.

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