The most useful Linux command line tricks

Anyone using the Linux command line met with lists of helpful tips. Everyone knows that everyday affairs can be performed more efficiently, but only this knowledge alone, not supported by practice, is of no use to anyone.

What do the typical work days of a system administrator sitting on Linux look like? If to abstract from everything, except the commands typed on the keyboard, it will appear that these commands constantly repeat. Everything goes to the level of automatism. And, if even in the work there is something to improve, the habit resists the new. As a result, a lot of time is spent on doing things as usual, and not as quickly, and, after a short period of habituation, it is more convenient. To keep this in mind, to consciously introduce new useful trifles into one’s own practice means to grow and develop professionally, which means saving time, which can be a lot of things to spend.


Before you - a small list of useful techniques for working with the Linux command line. You may already be familiar with some of them, but have managed to forget them. And something may well be a pleasant find even for connoisseurs. I would like to hope that some of them will be useful to you and will turn from a “list” into live commands that you will use every day.

The output of the results of the teams in a table

Sometimes the output of command output looks like a jumble of messy lines. You can find what you need in such data, but it is inconvenient to work with them. For example - something similar can be obtained in response to the mount command. It would be nice to display the same thing in the form of a table. And this is not only possible, but also very simple:
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 mount | column –t 

The results of the command mount, decorated in a table

By default, the command generates a table view, focusing on the spaces between words. And what if other characters are used as delimiters, like colons? For example - in the output cat /etc/passwd ?

You can also sort such data - it is enough to specify the separator character with the –s parameter. For example, below is the command for the ":" symbol.

 cat /etc/passwd | column -t –s: 

Formatted / etc / passwd output

Repeating a command multiple times before successful completion.

If you google on this topic, you will find that many are asking how to repeat a command until it is successfully completed. For example, this may be useful when pinging a server until it responds, when checking file uploads, or when polling a certain URL until it is available.

The while true cycle will help solve this problem. It looks like this:


The command will be repeated until successful completion.

In this example, the >/dev/null 2>&1 redirects the output of the program to /dev/null , including both Standard Error and Standard Out.

Most likely, this is one of the most useful techniques for working with the Linux command line.

Sorting processes by memory used

Everything is simple:

 ps aux | sort -nk 4 

Sorted process list

Sorting processes by using CPU resources

Sorting processes using CPU is done like this:

 ps aux | sort -nk 3 

Sorted process list

To get information about the architecture, use the getconf LONG_BIT .

Simultaneous viewing of several log files

The tail command is quite suitable for viewing log files, but sometimes you may need to work simultaneously with several similar files. To solve this problem, the multitail console tool is multitail , which supports text selection, filtering and many other useful features.


Work with multitail

Install this utility, if you do not find it, you can use the command apt-get install multitail .

Return to the previous directory

To return to the previous directory, just type cd –.

Monitoring at regular intervals

Using the watch utility (for example, watch df –h ) will help organize the monitoring of the output of any command. For example, you can monitor the amount of free space, and how it changes.

Perhaps you yourself will be able to find suitable scripts for using this command.

The continuation of the program after the session

When you run any program in the background and close the console, the program will also exit. What if it is necessary for the program to work even after the shell is closed?

In order to achieve this, you can use the command nohup , whose name stands for "no hang-up". It looks like this:

 nohup wget site.com/file.zip 

Perhaps this command is one of those that is most often forgotten, opening several windows of the terminal just for the sake of the commands executed in them.


Nohup command

In the example shown in the figure above, the file nohup.out will be created in the current directory, containing the output of the command:


Nohup.out file

Useful thing, agree?

Auto answer yes or no

Suppose you want to automate a process that requires the user to constantly answer yes . This can be done using the yes command:

 yes | apt-get update 

You may instead decide to automate negative responses. This design will help:

 yes no | command 

Automate Answer YES

Creating a file of a given size

You can create files of a given size using the dd :

 dd if=/dev/zero of=out.txt bs=1M count=10 

The above command will create a 10 MB file filled with zeros.


Creating a file of a given size

Execution of the last command with root privileges

Sometimes you can forget to enter sudo before a command that needs root privileges. There is no need to re-enter everything - just use this command:

 sudo !! 

Execution of the last command with root privileges

Creating a terminal session protocol

In order to write to the file everything that was displayed in the terminal window, you can use the script command.

After exiting the session, the protocol will be recorded in the typescript file.

Replacing spaces with tabs

Here is the command that allows you to replace spaces with tabs:

 cat geeks.txt | tr ':[space]:' '\t' > out.txt 

In fact, it is universal and can work with any characters.

Replacing lowercase letters to uppercase

And here is an example of the above command for replacing lower case letters in a text file with upper case letters:

 cat myfile | tr az AZ > output.txt 

Replacing lowercase letters in the file to uppercase

Automatic generation of argument list for commands: xargs

The xargs utility is probably worthy of the title of one of the most useful Linux command line features. It can be used to transfer the output of some command as an argument to another. For example, here’s how you can search for .png files and compress them, or do something else with them:

 find. -name *.png -type f -print | xargs tar -cvzf images.tar.gz 

Or, perhaps, you have a file with a list of URLs, and you want to upload resources to these addresses, or somehow process them:

 cat urls.txt | xargs wget 

Here we must bear in mind that the output of the first command is passed as an argument at the end of the xargs command. If, when constructing the second command, you must explicitly specify the place where the output data of the first one should go, it is enough to use a pair of curly braces, {} and the –i parameter to replace the argument in the right place:

 ls /etc/*.conf | xargs -i cp {} /home/likegeeks/Desktop/out 

Xargs command

Results

Linux command line utilities are an incredibly extensive topic. Therefore, any list like ours can be replenished for a very, very long time. For example, many unexpected things are hidden in the awk and sed commands. Perhaps the most important thing is for such lists to be in business.

And what interesting techniques do you use on the command line?