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Must Know Linux/Unix Commands
File Management becomes easy if you know the right commands.
Sometimes, commands are also referred as “programs” since whenever you run a command, actually, it’s the corresponding program code, written for the command, which is being executed.
Let’s learn the must know Linux commands.
Listing files (ls)
If you want to see the list of files on your UNIX or Linux system, use the ‘ls’ command.
It shows the files /directories in your current directory.
Directories are denoted in blue color.
Files are denoted in white.
You will find similar color schemes in different flavors of Linux.
Suppose, your “Music” folder has following sub-directories and files.
You can use ‘ls-R’ to shows all the files not only in directories but also subdirectories
NOTE: The command is case-sensitive. If you enter, “ls – r” you will get an error
‘ls -al’ gives detailed information of the files. The command provides information in a columnar format. The columns provide the following information:
File type and access permissions
Memory blocks occupied by file
Owner and the creator of the file
Group of the owner
File size in Bytes
Date and Time
Directory or File name
Let’s see an example -
Listing Hidden Files
Hidden items in UNIX/Linux begin with -at the start, of the file or directory.
Any Directory/file starting with a ‘.’ will not be seen unless you request for it. To view hidden files, use the command
ls - a
Creating & Viewing Files
The ‘cat’ command is used to display text files. It can also be used for copying, combining and creating new text files. Let’s see how it works
To create a new file, use the command
cat > filename
Press ‘ctrl + d’ to return to command prompt.
To view a file, use the command -
Let’s see the file we just created –
Let’s see another file sample2
The syntax to combine 2 files is -
cat file1 file2 > newfilename
Let’s combine sample 1 and sample 2.
As soon as you insert this command and hit enter, the files are concatenated, but you do not see a result. This is because Bash Shell (Terminal) is silent type. It will never give you a confirmation message like “OK” or “Command Successfully Executed”. It will only show a message when something goes wrong or when an error has occurred.
In order to view the new combo file “sample” use the command
Note: Only text files can be displayed and combined using this command.
The ‘rm’ command removes files from the system without confirmation. To delete a file use syntax -
Moving and Re-naming files
In order to move a file, use the command
Suppose we want to move the file “sample2” to location /home/guru99/Documents. Executing the command
mv sample2 /home/guru99/Documents
mv command needs super user permission. Currently, we are executing the command as a standard user. Hence we get the above error. To overcome the error use command
Sudo program allows regular users to run programs with the security privileges of the superuser or root.
Sudo command will ask for password authentication. Though, you do not need to know the root password. You can supply your own password. After authentication, the system will invoke the requested command.
Sudo maintains a log of each command run. System administrators can trackback the person responsible for undesirable changes in the system
For renaming file:
mv filename newfilename
NOTE: By default, the password you entered for sudo is retained for 15 minutes per terminal. This eliminates the need of entering the password time and again.
Enough with File manipulations! Let’s learn some directory commands
Directories can be created on a Linux operating system using the following command
This command will create a subdirectory in your present working directory, which is usually your “Home Directory”.
If you want to create a directory in a different location other than ‘Home directory’, you could use the following command -
will create a directory ‘Music’ under ‘/tmp’ directory
You can also create more than one directory at a time.
In order to remove a directory, use the command -
will delete the directory mydirectory
Tip: Ensure that there is no file / sub-directory under the directory that you want to delete. Delete the files/sub-directory first before deleting the parent directory.
The ‘mv’ (move) command (covered earlier) can also be used for renaming directories. Use the below given format:
mv directoryname newdirectoryname
Let us try it:
Other Important Commands
The ‘Man’ command
Man stands for manual which is a reference book of a Linux operating system. It is similar to HELP file found in popular softwares.
To get help on any command that you do not understand, you can type
The terminal would open the manual page for that command.
For an example, if we type man man and hit enter; terminal would give us information on man command
The History Command
History command shows all the commands that you have used in the past for the current terminal session. This can help you refer to the old commands you have entered and re-use them in your operations again.
The clear command
This command clears all the clutter on the terminal and gives you a clean window to work on, just like when you launch the terminal.
Pasting commands into the terminal
Many a times you would have to type in long commands on the Terminal. Well, it can be annoying at times, and if you want to avoid such a situation then copy, pasting the commands can come to rescue.
For copying, the text from a source, you would use Ctrl + c, but for pasting it on the Terminal you need to use Ctrl + Shift + v. You can also try Shift + Insert or select Edit>Paste on the menu
Below is a summary of commands we have learned in this tutorial
Lists all files and directories in the present working directory
ls – R
Lists files in sub-directories as well
Lists hidden files as well
Lists files and directories with detailed information like permissions , size , owner etc.
cat > filename
Creates a new file
Displays the file content
cat file file2 > file3
Joins two files (file1, file2) and stores the output in a new file (file3)
mv file “new file path”
Moves the files to the new location
mv filename new_file_name
Renames the file to a new filename
Allows regular users to run programs with the security privileges of the superuser or root
Deletes a file
Gives help information on a command
Gives a list of all past commands typed in the current terminal session
Clears the terminal
Creates a new directory in the present working directory