Linux basic commands with examples

Cat Command
Definition and purpose:
Cat command is used to display the content of a file or multiple files.
This command is more helpful in reading the log file or configuration files of the application or
system.
Syntax:
Cat file-name1 file-name2
Example:
Cat /etc/passwd
The above command displays the user's details that are available on the machine.
The primary usage of Cat command is for displaying the file content on the terminal window but
with Cat command, we can create files and add content also.
Most practical use is for:
 Checking the Application logs or system logs
 Concatenate two files or log files information and push to another file.
 Copying the content from one file to another file.
 Copying the content from one file to another file along with standard input from the terminal.
 To empty the file for having new content in it.
Below we have talked about few cat command options and their usage with practical examples.

Example-1:
Creating a new file with cat command:
Syntax:
“cat > filename”
Once the above command is typed and press enter. We see the cursor blinking on the next line, i.e,
whatever we may type here, that will be redirected to that file.
Check out the below example,
[rreddy@abclearn abclearn_dir1]$ cat > abc_lab3.txt
Hi
this information saves in new file
3rd line
- must be working
this is 5th line for testing
Note:
 we have to press “ctrl+d” to come out of file writing.
 If the file is not created already then it will be created with the user credentials.
 If the file is already existing, then its content is overwritten.
 So using “>” symbol we can redirect the information to given file.
We can use the same cat command to display files content.
To display content of abc_lab3.txt file,
Cat abc_lab3.txt

We have created a new file. Now, what if we want to add more lines to that existing file.
Example-2:
Add new lines to existing file:
Syntax:
Cat >> filename
Note1:
 “>” symbol is used to redirect the information into a file.
 “>>” symbol will add new text at the end of existing file.If the file doesn’t exist already, then
it is created.
We can add more information to existing file at the end using “>>” symbol.
[rreddy@abclearnabclearn_dir1]$ cat >>abc_lab3.txt
this is going to be as 6th line
7th one
8th one
Let’s see the file content and confirm, it is really added.
[rreddy@abclearnabclearn_dir1]$ cat abc_lab3.txt
Hi
3rd line
- must be working
7th one
8th one
Example-3:

Copy a file’s content to another file:
Syntax:
Cat source-file-name > target-file-name
As discussed earlier, “>” symbol will redirect the content which should be displayed on terminal
window to another file.
So source file content is not removed at all. It is simply redirecting the file content to another file
instead of on terminal.
We can use the cat command with “>” symbol to copy the content to another file and ">>" to append
at the bottom of another file.
[rreddy@abclearnabclearn_dir1]$ cat abc_lab3.txt > abc_lab4.txt
Hi
3rd line
- must be working
this is 5th line for testing this is going to be as
6th line
7th one
8th one
Example-4:
Display more than one file or multiple files output on terminal:
Cat command can concatenate one or more files content and show the output on the terminal.
Syntax:
Cat file-name1 file-name2
Let’s see a practical example for better understanding.

[rreddy@abclearnabclearn_dir1]$ cat abc_lab1.txt abc_lab2.txt abc_lab3.txt
this line should replace the existing one
this is the first line in new file
Hi
3rd line
- must be working
7th one
8th one
Example-5:
Redirect multiple files output to another file ( or ) concatenate more than one file output in
another file:
Following the explanations are given in above examples, we will make use of “>” symbol for
redirecting to file and “>>” symbol for adding the new content at the bottom of the target file.
Syntax:
Cat file-name1 file-name2 > file-name3
Cat file-name1 file-name2 >> file-name3
[rreddy@abclearnabclearn_dir1]$ cat abc_lab1.txt abc_lab2.txt abc_lab3.txt
> abc_lab4.txt
this is first line in new file
Hi
3rd line
- must be working

7th one
8th one
Example-6:
Display the line numbers of a file on terminal:
we have a couple of options with cat command to display output with line numbering.
Syntax:
Cat -n file-name
-n will display the line numbers including the empty lines.
Observe the below practical example and see line number 12 & 14. They are empty lines.
[rreddy@abclearnabclearn_dir1]$ cat -n abc_lab4.txt
1 this line should replace the existing one
2 this is first line in new file
3 Hi
4 this information saves in new file
5 3rd line
6 - must be working
7 this is 5th line for testing
8 this is going to be as 6th line
9 7th one
10 8th one
11 I am good
12
13 How are you
14
15 closing this file here
Example-7:
Display line numbers of a file but avoid empty lines:

For avoiding the empty lines from displaying in a file, we have command option is, “-b”
Syntax:
Cat -b file-name
Let’s look at the below cat command example, which completely avoids displaying the empty files.
[rreddy@abclearnabclearn_dir1]$ cat -b abc_lab4.txt
1 this line should replace the existing one
2 this is first line in new file
3 Hi
4 this information saves in new file
5 3rd line
6 - must be working
7 this is 5th line for testing
8 this is going to be as 6th line
9 7th one
10 8th one
11 I am good
12 How are you
13 closing this file here
Example-8:
Display or concatenate 2 files content with terminal one and standard input:
As we have discussed earlier, cat command comes with lot of options for variety of information.
We can take files information and concatenate it with terminal input.
Syntax :
Cat filename1 – filename2
“-“ option is to support input information from terminal or standard input also.

See the below example and try it out on terminal window,
[rreddy@abclearnabclearn_dir1]$ cat abc_lab1.txt - abc_lab2.txt
this line should replace the existing one---------------------------------
-->abc_lab1.txt file content
hi------------------------------------------------------------------------
-->information typed on terminal
hi
new lines
new lines
sadfa
sadfa
this is first line in new file--------------------------------------------
--->abc_lab2.txt file content
Example-9:
Emptying the file having the content:
In such cases we need to empty the files to reduce the utilization of the storage in the machine.
Syntax:
Cat /dev/null > File-name
[rreddy@abclearnabclearn_dir1]$ cat /dev/null > abc_lab2.txt
Exploring more cat command options:
For more on command options and their understanding, check out the manual pages or help content
given with cat command.
Syntax:
man cat
cat --help
info cat

Topics Summary
1.What are the practical use cases of cat command?
2.How to create a new file with cat command?
3.The command to add new lines to existing file?
4.Can we use the cat command to copy a file's content to another file?
5.How to display multiple file's outputs using cat command?
6.Instead of displaying the multiple files output on terminal, redirect it to a file. how can we achieve
this?
7.Command to display the line numbers of a file?
8.Command to display line numbers of a file but avoid empty files?
9.Is it possible to empty a file using cat command?
10.Is it possible to display 2 files output mixed with terminal input content?
cp command
Definition and purpose:
The primary usage of cp command is to “copy” files or directory from one location to another.
On Linux and UNIX flavor machines cp command is one of the most used commands in the day to
day activities.
Syntax:
cp source-file-name target-file-name
Example:

copying the file1 information to file2 within the same directory.
cp file1 file2
More about cp command and its options, please checks its manuals and help content.
Syntax:
 man cp
 cp –help
 info cp
Practical usages:
 Using the backup of a file or directory during installation and upgradations.
 Making a copy of a files content to another file.
 Moving the log files from one location to another location.
Example-1:
Copy content of a file to another file in the same directory:
This is the most practical use case of cp command.
Sometimes, we might want to do some changes to any application configuration file, then it’s always
a best practice to take a copy of that file content. This will act as a backup file.
Syntax:
Cp Source-file-name target-file-name
In the below given example, we want to copy “abc_lab1.txt” file content to “abc_lab1_copy.txt” .

[rreddy@abclearnabclearn_dir1]$cp abc_lab1.txt abc_lab1_copy.txt
[rreddy@abclearnabclearn_dir1]$ cat abc_lab1_copy.txt
Note:
 Here, an abc_lab1_copy.txt file is created newly. If this file already exists on the directory,
then it will be overwritten by default.
Example-2:
Copy the file content but don’t override the existing one:
We can use cp command in combination with “-n” option.
This file will copy the source file to destination file without disturbing or overwriting the original
content of destination file.
Therefore the final content of the destination file is source file content plus destination file content.
Syntax:
cp -n source-file target-file
Let’s observe a practical example.
There is a file and it is having all ftp user details. We have a copy of ftp user details of another
system as well. Now, my task is to combine all the users details in the single file.
In this scenario, we will use this option "-n".
Example Output:
[rreddy@abclearnabclearn_dir1]$cp -n abc_ftp1.txt abc_ftp2.txt
cp: overwrite ‘abc_ftp2.txt’? y
[rreddy@abclearnabclearn_dir1]$cat abc_ftp2.txt

Example-3:
Copy the file from one directory to another directory:
Syntax:
cp source-file-name Target-directory
Let us take a practical case,
As part of version upgrade for an application software, “app1_config.txt” and other configuration
files in installation directory are going to be updated to new format.
So we want to take a copy of these files, in another directory “/opt/bin/App1_Config_backup/” for
any roll back activity.
[rreddy@abclearnApp1_Config]$ cpapp1_config.txt
/opt/bin/App1_Config_backup/
Changing to target directory,
[rreddy@abclearnApp1_Config]$ cd /opt/bin/App1_Config_backup/
[rreddy@abclearnApp1_Config]$ ls
app1_config.txt
Note-1:
Here, App1_Config_backupdirectory should be created already. If it doesn’t exist, then will throw an
error.
[rreddy@abclearnApp1_Config]$ cp app1_config.txt
/home/rreddy/abclearn_dir2/
Note-2:

If we miss the last “/” shown in the red mark, instead of copying the content to dir2, there will be a
new file created with the name as abclearn_dir2 under rreddy directory.
Also note that, to copy a file or create a new file user should be having proper credentials to that
parent directory.
Example-4:
Copy entire directory to another directory:
Syntax:
cp -r Source-directory-name targer-directory-name
We can use the cp command with option “-r” recursive and copy entire directories and its sub-
directories to another directory.
[rreddy@abclearn~]$cp -r abclearn_dir1/ /tmp/
[rreddy@abclearn~]$ cd /tmp
[rreddy@abclearntmp]$ ls
Recursive copy means, first sub directories and their files are copied and in the last parent directory
is copied.
Example-5:
Forcing the copy operation:
While copying the file from one location to the another location it will ask for the confirmation by
using the cp command with '-f' option won’t prompt the confirmation.
Syntax:
cp -f source_file Target _directory

[rreddy@abclearnabclearn_dir1]$cp -f abc_lab1.txt /tmp
[rreddy@abclearn~]$ cd /tmp
[rreddy@abclearntmp]$ ls
Example-6:
Prompting when overwriting a file:
Whenever we are copying the content of one file to the another file there is a chance of losing the
important data in the destination file.
By using the cp command with "-i" option we get confirmation alert while overwriting the
destination file with the source file.
Syntax:
cp -i source_file Destination_file
[rreddy@abclearnabclearn_dir1]$cp -i abc_lab1.txt abc_lab1_copy.txt
cp: overwrite `abc_lab1_copy.txt'? y
[rreddy@abclearnabclearn_dir1]$cat abc_lab1_copy.txt
Example -7:
Copying the file to the directory without changing the attributes of the file:
While copying the file from one location to the another location the attributes like timestamp of the
file in the target location will change.
Without disturbing the attributes of the file we can copy the file from source to target using "-p"
option.
Syntax:
cp -p source_file Destination_directory

Follow the following scenario to understand more.
[ rreddy@abclearn ~]# cat abc_lab1.txt
[rreddy@abclearn~]# ls -l abc_lab1.txt
-rw-r--r--. 1 rreddy rreddy 0 Mar 21 19:32 abc_lab1.txt
[rreddy@abclearn~]# cp abc_lab1.txt /tmp
[rreddy@abclearn~]# cd /tmp
[rreddy@abclearn~]# ls -l abc_lab1.txt
-rw-r--r--. 1 rreddy rreddy 0 Jul 26 15:21 abc_lab1.txt
More to practice:
-u, --update copy only when the SOURCE file is newer
then the destination file or when the
destination file is missing
-s, --symbolic-link make symbolic links instead of copying
-H follow command-line symbolic links in SOURCE
-l, --link hard link files instead of copying
-L, --dereference always follow symbolic links in SOURCE
-a, --archive same as -dR --preserve=all
--attributes-only don't copy the file data, just the attributes
--backup[=CONTROL] make a backup of each existing destination file
-b like --backup but does not accept an argument

Topics Summary
1.During which situations, we use copy command as Linux administrator?
2.How to make a copy of a file into the same directory?
3.How to copy a file to another file but avoid overwriting if it's already existing?
4.How to copy a file from current directory to new directory?
5.How to force the copying operation?
6.How to copy entire directory to another directory?
7.Which flag or option of cp command can be used to prompt the file overwriting?
8.How to copy the file from one location to another location without changing the file attributes?
mv command
Linux mv command practical examples
In Linux and UNIX flavors, mv command has multiple advantages.
1. It can be used for moving the files from one directory to another directory. Like cut & paste
option, we usually have on word documents.
2. It can also be used for renaming a file in a given directory.
Note:
 There is no other command in Linux/Unix for renaming the files & directories.
 mv command can’t rename a directory.
Syntax:
mv source-file-name target-file-name

mv source-file-name target-directory
Let us understand this command practical use cases with below examples.
Example-1:
Rename a file in a directory:
[rreddy@abclearn abclearn_dir2]$ ls
abc_lab1.txt
[rreddy@abclearn abclearn_dir2]$ mv abc_lab1.txt newfile.txt
newfile.txt
Move a file from one directory to another directory
This mv command will remove the file from present directory and will made available in new
directory.
[rreddy@abclearn abclearn_dir1]$ mv abc_lab1_copy.txt
/home/rreddy/ebclearn_dir2/
If we check under abclearn_dir1 then file should be removed,
abc_lab1.txt abc_lab2.txt abc_lab3.txt abc_lab4.txt
the same file is available under abclearn_dir2.
[rreddy@abclearn abclearn_dir1]$ ls /home/rreddy/abclearn_dir2/
abc_lab1_copy.txt newfile.txt

Observe:
If we know the directory path, then check directory content using ls command, without changing into
it.
Move one directory as subdirectory to another
Couple of more options to try
Promoting options
-u, --update
Move only when the SOURCE file is newer than the destination file or when the destination file is
missing
-b like --Backup but does not accept an argument
Topics Summary
1.What is the use cases of mv command?can we rename a particular directory using mv command?
2.How to rename a file in a directory?
3.How to move a file from one directory to another directory?
4.How to make a directory as sub-directory to another? For ex: dir1 should be sub-directory for dir2.
WC Command
WC Command Examples
Practical purpose:

Most of the times, when we work with scripting programs,
we might encounter with a requirement of counting the number of lines of a file for writing the logic.
We may want to count the lines/words/characters of a command output.
This kind of requirements are best addressed by “wc command”.
wc command syntax:
wc file-name
wc file-name1 file-name2
Example-1:
Checking the lines,words and characters in a file:
[rreddy@abclearn abclearn_dir1]$ wc abclearn_lab1.txt
1 7 42 abclearn_lab1.txt
From the output,
1st column represents number of line in file
2nd column represents number of words in file
3rd column represents number of characters in file.
Example-2:
Counting the words in a file or in a content:
[rreddy@abclearn abclearn_dir1]$ wc -w abclearn_lab1.txt
7 abclearn_lab1.txt
Example-3:
Counting the lines in a file or in an output:

[rreddy@abclearn abclearn_dir1]$ wc -l abclearn_lab4.txt
15 abclearn_lab4.txt
We can also count number of line in more than one file, also.
[rreddy@abclearn abclearn_dir1]$ wc -l abclearn_lab4.txt abclearn_lab3.txt
8 abclearn_lab3.txt
23 total
Example-4:
Printing the byte counts of the file:
By using "-c" option with wc command we can print the byte counts of a particular file.
[rreddy@abclearn abclearn_dir1]$ wc -c abclearn_lab4.txt
Example-5:
Printing the length of largest line:
By using "-L" option with wc command we can print the length of largest line of a particular file.
[rreddy@abclearn abclearn_dir1]# wc -L abclearn_lab4.txt
Example -6:
Printing the new line count or Line count:
By using "-l" option with wc command we can print the new line (/n or enter) count of the particular
file.
[rreddy@abclearn abclearn_dir1]$ wc -l abclearn_lab4.txt
Topics Summary

1.What are some real time situations in which we use wc command?
2.How to check lines, words and characters of a file?
3.How to count the words in a file or an input content?
4.Which command we use for counting number of lines in a file?
5.How to print the byte or character count of a file?
6.What is the command to print length of longest line in a file?
rmdir and rm command
Linux rmdir and rm command examples
In this section, we will look at more on how to remove a file or directory on the Linux/UNIX flavor
machines.
Let’s start with rmdir command.
This is used for removing of an empty directory. An empty directory means, having no files and
subdirectories in it.
Syntax:
rmdir directory-name
rmdir command execution,
[rreddy@abclearn abclearn_dir1]$rmdirabclearn_dir2/
In practical, we don’t use this rmdir command so frequently. Main reason is,
Most of the times, every directory will be having at least few files and subdirectories under it. So to
use this command, we have to manually eliminate each and every file and subdirectory of it. which is
a tedious task.

The best solution is using “rm command” with “-rf” option.
rm command:
rm command is primarily used to remove single or multiple files under a directory.
Syntax:
rm file-name
Let’s understand some of its practical usages with examples.
Example-1:
Removing a particular file:
Removing a file is a straightforward requirement and there are so many of the cases for this.
Some practical usage cases,
We have worked on a sample file and want to delete after its usage.
We might find a corrupted configuration file and want to remove it and copy a new file from backup.
Syntax:
rm filename
sample rm command output is given below,
[rreddy@ebclearn ebclearn_dir1]$rm abc_lab1.txt
The one problem is, it will be removing the file without even prompting and once the file is deleted
in Linux/UNIX flavor OS, we can’t pull it back.
So always best practice is to prompt for deletion of a file.

rm command with “-i” option, will prompt the user whether to delete a file or not.
[rreddy@abclearn abclearn_dir1]$rm -i abc_lab2.txt
rm: remove regular file ‘abc_lab2.txt’? y
Example-2:
Force removing a file:
We can remove the file using "-f" command with rm command it won't prompt for confirmation to
delete it or not.
Syntax:
rm -f filename
Observe the following case for the proper understanding.
[rreddy@abclearn abclearn_dir1]$rm -f abc_lab2.txt
Example-3:
Removing multiple files at a time:
For removing multiple files, we will use rm command followed by file names
Syntax:
rm -i file-name1 file-name2
Observe the following usage for more understanding.
[rreddy@abclearn abclearn_dir1]$rm -i abc_lab2.txt abc_lab3.txt

For example:
If we want to delete all files under a particular directory using rm command, we can use directory
name followed by a star as indicated below.
$ rm -rf Directory_Name/*
Practical usage case,
We might want to remove files from /tmp directory for memory free.
[rreddy@abclearn~]$ rm -rf /tmp/*
Example-4:
Removing a directory with files and subdirectories under it:
We can remove the directory including directories and files in the particular directory using rm
command with "-r" option in this r indicates recursive.
Syntax:
rm -rf directory-name
Practical usage case,
Suppose a package is uninstalled/ removed from the system but the files and directories used by that
package will be there and consume some amount of storage. to free that storage we will remove that
directory with "rm -rf' command
[rreddy@abclearn~]$ rm -rf abc_lab
Example-5:
Removing the files having the same extension:

In some cases, we need to remove all files having the same extension. we use wild cards in these
scenarios.
to understand more follow the following scenario.
[rreddy@abclearn~]$ ls *.txt
a.txt b.txt c.txt d.txt
[rreddy@abclearn~]$ rm -i *.txt
rm: remove regular empty file `a.txt'? y
rm: remove regular empty file `b.txt'?
Possible issues we might face while removing a file or directory:
1. We need to have proper privileges on that directory or file in order to delete the file or directory.
2. Sometimes the filename which we are going to delete may end with space or tab. Include those
white space characters while deleting the file.
Topics Summary
1.How to remove an empty directory?
2.How to remove directory or a directory with subdirectories and files in it?
3.How to remove a file in a directory?
4.How to remove a file forcefully?
5.Command to remove multiple files at a time?
6.I have a couple of files in a directory and few of them have same extensions. How can we remove
those files with same extensions?
su command

su command practical examples
As we work through Linux administration activities, we most of the times have to switch between
one user credentials to another user credentials.
In this section, we will look at those requirement and command operations.
su command:
su is abbreviated as “switch user”.
Syntax:
su user-account-name
Throughout this section, we will understand about this command implementation with different
example scenarios.
Note:
sudo & su both commands are different in nature.
To understand more about sudo command, How can use sudo command for file executions?
Before we get started with examples, let us understand specific lookout areas of user identification.
Once we login to terminals, let’s check with what credentials I have logged into and what is my
default directory.
[rreddy@abclearn rreddy]$pwd
/home/rreddy
Looking at the command terminal in XXX shell,
 We can see userid specified before the server name.

Also “$” dollar symbol indicates that we have logged in as a non-root user.
Example-1:
Switch from one user to another user:
Using su command, we can switch from one user to another user account.
From rreddy, let’s switch to another user account called user1. Type the password.
[rreddy@abclearn~]$su user1
Password:
[user1@abclearn rreddy]$ whoami
user1
we can see that from rreddy, now I have logged in as user1.
Checking with pwd command,
[user1@abclearn rreddy]$pwd
/home/rreddy
Note:
In the above output, only user account got switched but not logged into new user’s home directory.
Example-2:
Switch user with its login user’s home directory:
With the same su command, if we specify “-“ then we will be in new user home directory by default.
Syntax:
su – user-account-name
From rreddy, let’s switch to another user account called user1.

[rreddy@abclearn~]$su - user1
Password:
Last login: Fri July 15 20:38:37 EST 2016 on pts/1
[user1@abclearn user1]$whoami
user1
[user1@abclearn rreddy]$pwd
/home/user1
Note:
landing on to user’s home directory may have advantages like
we can directly start accessing the files and directories under his home directory. This will avoid
another “cd” command typing.
Also, assigns the default shell for this user.
[user1@abclearn ~]$ echo $SHELL
/bin/bash
How to check landing user’s home directory and default shell information?
From /etc/passwd configuration file, we can understand each user default home directory and default
shell.
[rreddy@abclearn~]$ grep user1 /etc/passwd
user1:x:1001:1001::/home/user1:/bin/bash
To come back to previous user account:
We can type in exit command to come out of user session. It will take you to the previous logged in
user session,
Or else, we can again use su command to switch to the corresponding new user session.
[user1@abclearn rreddy]$ exit
exit

Note:
o For a root user, the password is not required while switching to another user. By default, he/she can
switch to any user they want.
o If we have switched users a multiple number of times, then for each exit type control goes back to
the previous user account.
Example-3:
Changing the default user login shell:
Syntax:
su --shell shell-path user-account-details
Practical usage:
In Shell scripting programing….
Another example….
Sample command output,
[rreddy@abclearn~]$su --shell /bin/sh user1
Password:
sh-4.2$ echo $SHELL
/bin/sh
Example-4:
Switching to root user account:
Just like switching to a normal user, we can specify “root” user name for switching to it.

But, there is a special case also,
even if we don’t specify any user account details after su command, then by default, it will expect
root account credentials.
Syntax:
Su – root
su –
[rreddy@abclearn~]$su -
Password:
Last login: Fri Jan 15 02:31:24 EST 2016 on pts/3
[root@abclearn~]#pwd
/root
Note:
A root user can switch to any other account without even knowing the password of that user.
[root@abclearn~]#su user1
[user1@abclearn ~]$whoami
User1
Topics Summary
1.How to switch from one user to another user in Linux?
2.How to switch back to previous user account from present one? Or come out of present use
session?
3.How to switch to new user and landing into user’s home directory?
4.How can we change the new user SHELL form the default when logging in?
5.How can we switch to root user account in Linux environment?
Ls command

Ls command is used to list the files and subdirectories under a specific directory. It is one among the
regularly used commands while doing administration of a server.
Syntax:
ls
ls -l
ls -ltr
Above given are a couple of options which are most regularly used with ls command.
We will see some ls practical examples below for better understanding of it.
Example-1:
Listing the files and directories:
By typing normal ls command on the terminal window, will list all of the files and subdirectories
under a directory.
Sample Usage case,
Assume that we have a software package unzipped on Linux/Unix flavor machine. Now, to see what
are the files and sub-directories are available within that we can use this command.
We can take a numerous number of examples for “ls command”, above is just a sample case. Normal
“ls command” output is,
[root@sys1 repo]# ls
EFI media.repo RELEASE-NOTES-or-IN.html
EULA Packages RELEASE-NOTES-pa-IN.html
EULA_de README RELEASE-NOTES-pt-BR.html
EULA_en RELEASE-NOTES-as-IN.html RELEASE-NOTES-ru-RU.html
EULA_es RELEASE-NOTES-bn-IN.html RELEASE-NOTES-si-LK.html

Example-2:
Long listing of files and directories:
From the normal “ls command”, we could see only list of things available but it won’t show up more
details about it. Such as,
Whether it is a file or directory?
Who are the owner & group ownership of that file or directory?
What are the files permissions level and last modified dates? etc
We can see all of the above information from using “ls -l” command option.
Syntax:
ls -l
A sample command output is given below,
[root@sys1 repo]# ls -l
total 3120
-r--r--r--. 1 root root 11414 Jan 31 2013 TRANS.TBL
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 Server
dr-xr-xr-x. 3 root root 4096 Jan 31 2013
ScalableFileSystem
-r--r--r--. 1 root root 3211 Jan 29 2013 RPM-GPG-KEY-
redhat-release
redhat-beta
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 ResilientStorage
drwxr-xr-x. 2 root root 4096 Feb 8 13:50 repodata
From “ls -l” command output we can make out,
Starting from left,
The first character explains whether it is a file or directory.

Next, 9 characters explain what permission levels are for the user, primary group and others in
sequence.
Next character talks about file inode information.
Who are the primary owner and group owner of the files is explained?
File size and next time/date of file modified information.
Also, try,
ls -m
ls -x
Example-3:
Files with reverse order:
To display the files in reverse chronological order. We can use “-r” option with ls command.
Syntax:
Is-Ir
Note:
“-r” option should always use with “-l” option for better results.
One can observe that based on the file alphabetical order we can see the files organized. Sample
output is given below.
[root@sys1 repo]# ls -l
total 3120
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 Server
ScalableFileSystem
redhat-release

redhat-beta
ResilientStorage
Example-4:
Files and directories with timestamp and reverse timestamp:
For displaying the files and directories based on timestamp, we can use “-t” option with ls command.
Syntax:
Ls -lt
Sample command output is given below,
[root@sys1 repo]# ls -lt
total 3120
drwx------. 2 root root 16384 Feb 2 12:01 lost+found
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 images
dr-xr-xr-x. 2 root root 253952 Jan 31 2013 Packages
HighAvailability
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 LoadBalancer
We can combine -r option with -t timestamp, for files and directories in reverse timestamp.
Syntax:
ls -ltr
ls -l -t -r

This is most used on day to day life, because it gives the recent modified files and directories
information in the top order. Keep note of this for sure.
Sample ls -ltr command output is,
[root@sys1 repo]# ls -ltr
total 3120
drwx------. 2 root root 16384 Feb 2 12:01 lost+found
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 images
dr-xr-xr-x. 2 root root 253952 Jan 31 2013 Packages
HighAvailability
dr-xr-xr-x. 3 root root 4096 Jan 31 2013 LoadBalancer
Example-5:
Files and directories with human readable size format:
As we have discussed, ls -l command will display the files and directories size information also but
they are in blocks format. We need to convert them into kilo bytes and Mega bytes etc to understand
clearly.
Instead, we can use “-h” option with ls command to display the sizes in human readable format.
Syntax:
ls -lh
sample command output is given below,
[root@sys1 repo]# ls -lh
total 3.1M
dr-xr-xr-x. 3 root root 4.0K Jan 31 2013 EFI
lrwxrwxrwx. 1 root root 7 Jan 31 2013 EULA ->
EULA_en
-r--r--r--. 1 root root 11K Nov 7 2012 EULA_de
-r--r--r--. 1 root root 8.6K Nov 7 2012 EULA_en
-r--r--r--. 1 root root 11K Nov 7 2012 EULA_es

-r--r--r--. 1 root root 11K Nov 7 2012 EULA_fr
-r--r--r--. 1 root root 11K Nov 7 2012 EULA_it
-r--r--r--. 1 root root 13K Nov 7 2012 EULA_ja
-r--r--r--. 1 root root 9.7K Nov 7 2012 EULA_ko
-r--r--r--. 1 root root 9.8K Nov 7 2012 EULA_pt
-r--r--r--. 1 root root 7.2K Nov 7 2012 EULA_zh
Let’s remove the -l option and observe the output,
Ls -h command output here….
Similar to above we can try,
ls -s To display file sizes in bytes
ls -k To display file sizes in kilo bytes
ls -m To display file sizes in mega bytes
By using ls –s command we can do this.
[root@sys1 repo]# ls -s
total 3120
4 EFI 92 RELEASE-NOTES-fr-FR.html
0 EULA 80 RELEASE-NOTES-gu-IN.html
12 EULA_de 136 RELEASE-NOTES-hi-IN.html
12 EULA_en 84 RELEASE-NOTES-it-IT.html
12 EULA_es 100 RELEASE-NOTES-ja-JP.html
12 EULA_fr 156 RELEASE-NOTES-kn-IN.html
12 EULA_it 88 RELEASE-NOTES-ko-KR.html
16 EULA_ja 164 RELEASE-NOTES-ml-IN.html
12 EULA_ko 140 RELEASE-NOTES-mr-IN.html
Example -6:
Listing the hidden files and directories:
Regular ls command will not display any hidden files and sub directories under a directory. Let’s first
understand,

what is a hidden file or directory? And Why we need that in first place?
In a day to day activities we might want to hide critical/important files and directories from regular
user. This is just to avoid any accidental changes to those files etc.
for example, some application specific configuration files.
To hide a file or directory, we need to use “.” Before file/directory name.
Example, .profile, .bash_profile etc
To view these hidden files and directories, we can use “-a” option with ls command.
Syntax:
ls -a
ls -la
ls -lat
Sample command output is given below,
[root@sys1 repo]# ls -a
. lost+found RELEASE-NOTES-or-IN.html
.. media.repo RELEASE-NOTES-pa-IN.html
EFI Packages RELEASE-NOTES-pt-BR.html
EULA README RELEASE-NOTES-ru-RU.html
Example-7:
Listing out inode numbers with files and directories:
If you are new to inode numbers, then visit this, what are inode numbers? How they are associated
with files and directories structure?
Syntax:
ls -i ls -li

A usage case,
When do we check inode numbers for a files?
Practical command output is given below,
By using ls –I command we can do this
[root@sys1 repo]# ls -i
128001 EFI 3780 RELEASE-NOTES-fr-FR.html
12 EULA 3781 RELEASE-NOTES-gu-IN.html
13 EULA_de 3782 RELEASE-NOTES-hi-IN.html
14 EULA_en 3783 RELEASE-NOTES-it-IT.html
15 EULA_es 3784 RELEASE-NOTES-ja-JP.html
16 EULA_fr 3785 RELEASE-NOTES-kn-IN.html
17 EULA_it 3786 RELEASE-NOTES-ko-KR.html
18 EULA_ja 3787 RELEASE-NOTES-ml-IN.html
19 EULA_ko 3788 RELEASE-NOTES-mr-IN.html
20 EULA_pt 3789 RELEASE-NOTES-or-IN.html
21 EULA_zh 3790 RELEASE-NOTES-pa-IN.html
Topics Summary
1.How to list the files and directories in Linux/UNIX?
2.How to list the files and directories in the reverse order?
3.How to list the files with a timestamp and in reverse timestamp in Linux?
4.How to list the files with size in human reversible format?
5.Command to display the hidden files of a directory?
6.How list the files with their inode numbers in Linux?

Linux basic commands with examples

Linux basic commands with examples

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