Commands, Options and Arguments

The shape of a command

Most commands follow the same pattern:

command -options arguments

• The command is the program to run, for example ls.
• Options (also called flags) change how it behaves. They start with a dash: -l.
• Arguments tell the command what to work on, for example a file or folder name.

The parts are separated by spaces. Let's see it with ls, the command that lists files.

Just the command

ls

In the terminal

student@vulntech:~$ ls
Documents  Downloads  notes.txt  projects

ls on its own lists what is in the folder you are in. Folders are shown in blue in a real terminal.

Adding an option

The -l option asks for the long format, with details about each item:

ls -l

In the terminal

student@vulntech:~$ ls -l
total 2
drwxr-sr-x 2 student student  0 Oct 16 19:04 Documents
drwxr-sr-x 2 student student  0 Oct 16 19:04 Downloads
-rw-r--r-- 1 student student 30 Oct 16 19:04 notes.txt
drwxr-sr-x 2 student student  0 Oct 16 19:04 projects

Don't worry about all the columns yet; you will learn to read them in module 2. For now notice that the same command shows more because of the option.

The -a option shows all files, including hidden ones. On Linux, a file is hidden when its name starts with a dot:

ls -a

In the terminal

student@vulntech:~$ ls -a
.   .bash_profile  .hidden_note  Documents  notes.txt
..  .bashrc        .hushlogin    Downloads  projects

. and .. are special: they mean this folder and the folder above. You will use them a lot in module 2.

Combining options

You can give several options separately, or squeeze them together after one dash. These two commands do exactly the same thing:

ls -l -a
ls -la

In the terminal

student@vulntech:~$ ls -l -a
total 6
drwxr-sr-x 5 student student   0 Oct 16 17:44 .
drwxr-xr-x 3 root    root      0 Oct 16 17:44 ..
-rw-r--r-- 1 student student  32 Oct 16 17:44 .bash_profile
-rw-r--r-- 1 student student 669 Oct 16 17:44 .bashrc
-rw-r--r-- 1 student student   7 Oct 16 19:04 .hidden_note
-rw-r--r-- 1 student student   0 Oct 16 17:44 .hushlogin
drwxr-sr-x 2 student student   0 Oct 16 19:04 Documents
drwxr-sr-x 2 student student   0 Oct 16 19:04 Downloads
-rw-r--r-- 1 student student  30 Oct 16 19:04 notes.txt
drwxr-sr-x 2 student student   0 Oct 16 19:04 projects
student@vulntech:~$ ls -la
total 6
drwxr-sr-x 5 student student   0 Oct 16 17:44 .
drwxr-xr-x 3 root    root      0 Oct 16 17:44 ..
-rw------- 1 student student   9 Oct 16 19:04 .bash_history
-rw-r--r-- 1 student student  32 Oct 16 17:44 .bash_profile
-rw-r--r-- 1 student student 669 Oct 16 17:44 .bashrc
-rw-r--r-- 1 student student   7 Oct 16 19:04 .hidden_note
-rw-r--r-- 1 student student   0 Oct 16 17:44 .hushlogin
drwxr-sr-x 2 student student   0 Oct 16 19:04 Documents
drwxr-sr-x 2 student student   0 Oct 16 19:04 Downloads
-rw-r--r-- 1 student student  30 Oct 16 19:04 notes.txt
drwxr-sr-x 2 student student   0 Oct 16 19:04 projects

Long options

Many options also have a long, readable name that starts with two dashes. --all is the long name of -a:

ls --all

In the terminal

student@vulntech:~$ ls --all
.   .bash_profile  .hidden_note  Documents  notes.txt
..  .bashrc        .hushlogin    Downloads  projects

Adding an argument

An argument tells ls which folder to list:

ls Documents

In the terminal

student@vulntech:~$ ls Documents
welcome.txt

Options and arguments can be used together:

ls -l Documents

In the terminal

student@vulntech:~$ ls -l Documents
total 1
-rw-r--r-- 1 student student 16 Oct 16 19:04 welcome.txt

echo takes arguments too. Every word you give it is an argument, and it prints them all:

echo one two three

In the terminal

student@vulntech:~$ echo one two three
one two three

Common mistake: Spaces matter. ls -l is the ls command with the -l option, but ls-l (no space) is a command called ls-l, which doesn't exist.

Remember: command -options arguments. Short options use one dash (-a), long options use two (--all).