- Computers provide two kinds of interfaces to the user:
- Graphical User Interface (GUI), and
- text-based interfaces (through command line or terminal)
These interfaces allow you to navigate through the operating system and file system. In text-based interfaces, a command line interpreter or shell is used to interpret the given commands by the user. Bash allows users to provide commands through which the user can specify what they want to do. Before providing the commands, bash displays a prompt, as you open the command line (in Linux and macOS), such as the one below.
user@localhost:~$
This prompt would typically state the current username with the hostname of the system. By default, the current directory of the terminal will be the user's root (or home) directory.
echo-print
- echo is the most basic command in bash, which displays its arguments on standard output (on the terminal).
user@localhost:~$ echo "Hello World!"
Hello World!
user@localhost:~$ echo Hello World!
Hello World!
pwd- print working directory
- pwd is a command that stands for Print Working Directory. It displays your current working directory as output.
user@localhost:~$ pwd
/home/user
ls — List directory contents
- ls is a command short for list. It lists down the contents of a directory. By default, it lists the contents of the current working directory. From the example introduced at the start of the section, if we list down the contents of our current directory we get
user@localhost:~$ ls
Documents Pictures Videos
ls -a
- This option enables us to view hidden files. In the code block below, the files with a preceding dot ., are hidden files. These hidden files are not visible on GUI unless you enable the option to view them.
- user@localhost:~$ ls -a
- Documents Pictures .temp_file Videos .webpage
cd- change directory
- cd is a command to change directory. By providing a path along with this command, we can change the current directory to a different directory. This command does not give an output and only changes the directory. You can later use ls to display the directory contents to check that the current directory has been changed.
user@localhost:~$ cd Documents
user@localhost:~$ ls
file1.txt
user@localhost:~$ cd ..
user@localhost:~$ ls
Documents Pictures Videos
In the above example, we used a shortcut .. to change back to the parent directory. This can be used several times in a single path to go up the hierarchy of parent directories. Of course, you can provide the entire path to the directory as well.
Working with files means modifying them in any capacity. Renaming, moving, creating, and deleting new files are the basic operations when working with files. Let's have a look at these operations using bash in this section.
mkdir- make directory
- mkdir is a command short for Make Directory. It creates a new directory with the specified name.
user@localhost:~$ mkdir BashTutorial
user@localhost:~$ ls
BashTutorial Documents Pictures Videos
rmdir- remove directory
- rmdir is a command for Remove Directory. It removes the specified directory. It should be noted that the directory to be removed must be empty or the terminal will throw an error.
user@localhost:~$ mkdir BashTutorial
user@localhost:~$ ls
BashTutorial Documents Pictures Videos
touch- create blank file
- touch is a command used for creating blank files. This command only creates a blank file and does not add anything to it.
user@localhost:~$ touch Newfile
user@localhost:~$ ls
Documents Newfile Pictures Videos
rm- remove file
rm is the command for removing files. Similar to rmdir, this action cannot be undone so careful use is recommended.
user@localhost:~$ rm Newfile
user@localhost:~$ ls
Documents Pictures Videos
rm -r
- A helpful option available for rm is -r. Adding this option allows us to remove non-empty directories with ease, as it recursively goes through all the files and sub-directories inside a directory and deletes them.
user@localhost:~$ rmdir Videos
rmdir: failed to remove 'Videos': Directory not empty
user@localhost:~$ rm -r Videos
user@localhost:~$ ls
Documents Pictures
mv- moive file or directory
- mv is a command used to move a file or a directory. We can specify this using the syntax below, where source and destination are paths to the file or directory that needs to be moved.
user@localhost:~$ ls
Documents Pictures Videos example1
user@localhost:~$ mkdir NewFolder
user@localhost:~$ mv example1 NewFolder/
user@localhost:~$ ls
Documents NewFolder Pictures Videos
user@localhost:~$ cd NewFolder
user@localhost:~$ ls
example1
mv is a helpful command that can also be used for renaming files. If we specify the destination path the same as the source path, but with a different name, then we can rename the file.
user@localhost:~$ ls
Documents Pictures example1
user@localhost:~$ mv example1 linux_example
user@localhost:~$ ls
Documents Pictures linux_example
man — Print manual or get help for a command
- The man command is your manual and is very useful when you need to figure out what a command does. For example, if you didn’t know what the command rmdir does, you could use the man command to find that out.
less — view the contents of a text file
- The less command allows you to view files without opening an editor. It’s faster to use, and there’s no chance of you inadvertently modifying the file.
compgen — Shows all available commands, aliases, and functions
- compgen is a handy command when you need to reference all available commands, aliases, and functions.
head — Read the start of a file
- By default, the head command displays the first 10 lines of a file. There are times when you may need to quickly look at a few lines in a file and head allows you to do that. A typical example of when you’d want to use head is when you need to analyze logs or text files that change frequently.
tail — Read the end of a file
- By default, the tail command displays the last 10 lines of a file. There are times when you may need to quickly look at a few lines in a file and tail allows you to do that. A typical example of when you’d want to use tail is when you need to analyze logs or text files that change frequently.
exit — Exit out of a directory
- The exit command will close a terminal window, end the execution of a shell script, or log you out of an SSH remote access session.
history — list your most recent commands
- An important command when you need to quickly identify past commands that you’ve used.
clear — Clear your terminal window
This command is used to clear all previous commands and output from consoles and terminal windows. This keeps your terminal clean and removes the clutter so you can focus on subsequent commands and their output
cp — copy files and directories
- Use this command when you need to back up your files.