Piping and Redirecting Output in the Linux Terminal

Rob

Administrator
Staff member
Joined
Oct 27, 2011
Messages
1,222
Reaction score
2,284
Credits
3,574
Piping and redirection are two important techniques for controlling the output of terminal commands in the Linux environment. They allow you to perform complex operations and automate tasks with ease. In this article, we'll look at the basics of piping and redirection and how you can use these tools to become more efficient and productive.

Piping

Piping is a technique for sending the output of one command to another command. The basic syntax for piping is:

command1 | command2

Here, the output of "command1" is sent to "command2" as input. This allows you to perform multiple operations in one line, making it easy to automate tasks and streamline workflows.

For example, you could use the "ls -l" command to list the contents of a directory, and then pipe the output to the "grep" command to search for files with a specific extension:

ls -l | grep ".txt"

This will list only the files in the directory that have a ".txt" extension.

Redirection

Redirection is another technique for controlling the output of terminal commands. Unlike piping, which sends the output of one command to another command, redirection sends the output of a command to a file or to another device. The basic syntax for redirection is:

command > filename

Here, the output of the "command" is redirected to the file "filename". If the file already exists, its contents will be overwritten. If it does not exist, a new file will be created.

You can also append the output of a command to an existing file using the ">>" operator:

command >> filename

This will add the output of the "command" to the end of the file "filename", instead of overwriting it.

Another useful redirection operator is the "2>" operator, which allows you to redirect error messages to a file. For example:

command 2> error.log

This will send any error messages generated by the "command" to the file "error.log". This can be useful when you are troubleshooting an issue and need to see what error messages are being generated.

You can also use redirection to send the output of a command to another device, such as a printer or another computer. To do this, you can use the "|" operator and specify the device as the target. For example:

command | lp

This will send the output of the "command" to the default printer.

Using Piping and Redirection Together

Piping and redirection can be used together to perform complex operations. For example, you could use the "ls -l" command to list the contents of a directory, pipe the output to the "grep" command to search for files with a specific extension, and then redirect the output to a file:

ls -l | grep ".txt" > txt_files.log

This will create a file called "txt_files.log" that contains a list of all ".txt" files in the directory, along with their details.

Conclusion

Piping and redirection are two powerful tools for controlling the output of terminal commands in the Linux environment. By chaining commands together and redirecting output to files or other devices, you can perform complex operations and automate tasks with ease. Whether you're a seasoned Linux user or just getting started, mastering these concepts will help you become more efficient and productive in your work.

By the way, this article was written by ChatGPT - how'd it do? :)
 
Last edited:


I want to call you an idea stealer - but I never mentioned it. LOL I've played with ChatGPT a few times and planned (I might still do it) an article written by the bot just to show how far tech has come.

Meh... I might still do it.
 
It's absolutely amazing what you can get it to spit out. The writing can often pass for what I'd call natural writing, meaning looking like it came from a human.

We've come a long ways since the early Markov chain chat bots.
 
Very helpful write up on piping and redirecting, thanks!
 
  • Like
Reactions: Rob
Nicely done post.
But what happens if you leave out the quotes as thus...?
Code:
 ls -l | grep .txt
I tried it and I just get a blank output. What got grepped to where? Or is this just considered an error?
 
Nicely done post.
But what happens if you leave out the quotes as thus...?
Code:
 ls -l | grep .txt
I tried it and I just get a blank output. What got grepped to where? Or is this just considered an error?
You probably should put quotes around `.txt`, but it works without them in this case. If you had any files in that directory that ended in .txt you should see them with that command.
 
But what happens if you leave out the quotes as thus...?

You might want to read this:


It explains it better than I could ever explain it. Basically, do not parse the output of 'ls'. It can lead to a bunch of errors in the output. There are better solutions.

Edit: But, if you're going to (and I do it myself), you may find this is what you're after:

Code:
ls -la | grep *.txt
 

Staff online

Members online


Top