Your First Commands

Quick check: Do you know what pwd prints? If yes, skip to What Happens When You Type a Command.

Practice this topic: Terminal Basics skill drill

After this lesson, you will be able to:

• Run whoami, hostname, date, uname, cal, pwd, and ls
• Use flags (-a, -l, -la) to modify command behavior
• Explain the five-step process the shell uses to execute a command

Six Commands to Start With

Open your terminal and type each of these:

whoami          # your username
hostname        # machine name
date            # current date and time
uname -a        # OS and kernel info
cal             # this month's calendar
pwd             # current working directory

Each command does one thing. That is the Unix philosophy in action.

Flags Change Behavior

Most commands accept flags (short options starting with -):

ls              # list files in current directory
ls -a           # include hidden files (names starting with .)
ls -l           # long format (permissions, size, date)
ls -la          # both

From Java: In Java, you passed arguments to methods. In Unix, you pass flags and arguments to commands. ls -la /tmp is like calling ls.run("-la", "/tmp").

What Happens When You Type a Command

When you type ls and press Enter, five things happen:

1. The shell reads your input
2. The shell searches PATH for a program called ls
3. The shell asks the kernel to create a new process
4. The ls program writes to stdout (your screen)
5. The shell displays a new prompt

This is why ./hello requires the ./ — the shell only searches PATH directories, and . (the current directory) is not in PATH by default. You must tell it explicitly where to look.

Exploring with ls

ls -l

Output looks like:

drwxr-xr-x  2 student student 4096 Mar 30 09:00 Documents
-rw-r--r--  1 student student   42 Mar 30 09:00 notes.txt

What Comes Next

You can run commands and read output. Next: creating, moving, and organizing files and directories.