Important Linux commands for Devops

  ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Important Linux commands​​ for Devops

What you will Learn:

  • pwd

  • Change directory commands: ​​ cd, cd ~, cd -

  • List commands: ​​ ls, ls -l, ls -la, ls​​ lh, ls -lht,​​ ls​​ lhtr

  • touch command

  • cat command

  • tail command

  • head command

  • mkdir command

  • create multiple directories using -p switch

  • man command

  • cp command

  • rm command

  • Rename a file (mv command)

pwd

‘pwd’ command is used to print current working directory. This command tells us where we are in the file system at any point. When you execute ‘pwd’ command for the first time, it prints default home directory​​ 

cd​​ commands

‘cd’ is to change the directory

Now​​ if you execute ‘pwd’, the output shows / as expected

Similarly​​ 

Next,​​ cd ~​​ (cd tilde) switches you back to default home directory, irrespective of where you are in the current file system

Next, let us change directory to /home and then to /etc.

When you now execute​​ cd​​ -​​ it takes you back to previous directory (viz /home in current case)

ls commands

‘ls’​​ commands are used to list​​ the contents of current directory. The contents can be files or directories​​ 

‘ls –l’ is the long listing

Let us cd to /etc and execute the same command, you can see the details of files and directories​​ 

Now, ‘ls -l’ command does NOT show the hidden files and directories. To see the hidden contents, we use the ‘a’ switch viz ‘ls -la’. As you can now see, we can see the hidden files (files starting with dot are hidden files)​​ 

​​ 

Next, if you want to know the file size in human readable format, you can use ‘h’ switch viz ‘ls -lh’. So we can see below the file sizes (4K meaning 4 kilobyte, 3 kilobyte and so on)

Next,​​ ‘ls -lht’ sorts the files based on timestamps (latest file first) ​​ 

Next, ls -lhtr’ shows oldest file first ​​ 

The above 2 commands​​ can be used​​ to find latest/oldest log file.

touch command

‘touch command can be used to create a new file. Let us cd to home directory and execute ‘touch testfile.txt’ command. You can see that a blank file has been created

cat command

‘cat’ command can be used to view the contents of a file

Let us cd to /var/log​​ and​​ execute ‘cat syslog’.

As you can see below, we can see the file contents

tail command

If the file contents are huge, you might want to see only the last few lines. This is generally true when you want to see the latest​​ log file contents. So in order to see the only the last few lines of a log file, you can use the ‘tail’ command

head command

Similarly you can see the top few lines of a file using ‘head’ command

mkdir command

We can create a directory using mkdir command. Let us cd to home dir

create multiple directories using -p switch

Using -p switch you can create multiple directories hierarchy using a single command. As you can see below, d2 got created under d1 and d3 under d2

man command

You can use ‘man’ command to read the manual of any command. For example, ‘man ls’ will give you the complete manual of ‘ls’ command

You can scroll the manual by arrow down key

cp command

You can create a copy of a file using ‘cp’

Similarly, you can create a copy of directory using -r switch

rm command

‘rm’ command can be used to delete a file

Let us look at the manual of ‘rm’ command to find out how to delete a directory. After executing ‘man rm’, just type​​ /directory​​ at the bottom and hit enter. This will search all the keywords in the manual that match ‘directory’. See below, it tells us to use -r to remove a directory

This way, you don’t have to remove all the switches, simply use the ‘man’ command. Notice below that we have deleted the testdir2 directory

Rename a file (mv command)

To rename a file, simply use ‘mv’ command. Below we have renamed testfile2.txt to testfile4.txt

So these were very basic linux commands.

Thank you for reading!

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