Briefing Document: Linux Fundamentals - Week 4: Advanced Commands & Processes
This briefing highlights the key learning objectives, concepts, and commands for Week 4 of the "Introduction to Linux" course, focusing on powerful file searching, process management, and advanced command line interaction.
1. Week 4 Objectives The primary objectives for Week 4 are:
• Demonstrate finding files with several criteria.
• Show the use of ls with wildcards and recursive searches.
• Explain how to locate running processes and kill a process.
2. Understanding Command Structure In Linux, commands follow a specific "sentence structure": "Command Switch Argument".
• Command: The primary instruction (e.g., ls, find, kill).
• Switch (or Option/Flag): A dash (-) followed by a letter (e.g., -l, -r, -s). Switches enhance the command's power and detail.
    ◦ Case Sensitivity: Switches are case-sensitive; for example, -r is not necessarily the same as -R.
    ◦ Combining Switches: Multiple switches can often be combined (e.g., ls -la).
• Argument: An additional piece of information passed to the command, specifying what the command should act upon (e.g., a filename, a directory path, a Process ID). Some commands, like copy or move, require arguments.
3. Enhanced ls Command Usage The ls (list files) command can provide more detailed information using switches:
• ls -l: Displays a long list format, showing permissions, file sizes, dates, and other details.
• ls -a: Shows all files, including hidden files (those starting with a dot).
• ls -la: Combines the above, providing a long list format that includes hidden files.
4. Wildcards: Powerful Pattern Matching Wildcards are special characters that allow you to match patterns in filenames and directories, enabling more flexible and powerful commands.
• * (Splat/Asterisk): Matches any number of characters.
    ◦ Example: find all files that end in txt.
    ◦ Example: find all files that start with a through c followed by any number of characters could use [a-c]*.
• ? (Question Mark): Matches any single character.
• [] (Square Brackets): Indicates a set of characters.
    ◦ Example: [aA] matches 'a' or 'A'.
    ◦ Example: `` matches any digit.
    ◦ Combining: You can combine sets with other wildcards, e.g., [a-c]* to find files starting with 'a', 'b', or 'c'.
5. The find Command The find command is essential for searching for files based on various criteria.
• Basic Usage: find -name myfile.
• Within a Specific Folder: find /etc -name passwd (searches for 'passwd' within the /etc directory).
• By Extension: find -name “*.txt” (finds all files ending in .txt).
• Case-Insensitive: find -iname testfile (finds 'testfile' regardless of case).
• find can also search by other criteria such as groups, user, file type, directory, empty files, date, and last access.
6. Processes: Viewing and Managing Running Programs Processes are instances of running programs or commands in Linux.
• Viewing Processes:
    ◦ ps: Lists the processes that you own in the current terminal.
    ◦ ps -a: Lists all processes associated with your current session. (Many other options exist, consult the manual for ps).
• Killing Processes: The kill command is used to terminate a process.
    ◦ kill [process_id_number]: Requires the Process ID (PID) as an argument. The PID is generally a "semi large number".
    ◦ kill -9 [process_id_number]: This is a forceful termination, often called "kill with a big stick," used when a process is unresponsive to a regular kill command.
• Safe Practice: To practice killing processes, it's recommended to create "junk processes" using the sleep command: sleep [number_of_seconds] & (e.g., sleep 12345 &). The & makes the sleep command run in the background. Crucially, do NOT practice killing your own bash process, as this will log you out of the system.
7. Suggested Activities for Practice
• Wildcard Challenges: Go to a Linux emulator or machine and practice using wildcards to find files based on patterns like starting with specific letters (case-sensitive and insensitive), containing digits, or ending with certain characters.
• find Command Experimentation: Experiment with the find command, including searching within your home directory, by name, by extension, and case-insensitively.
• Process Management: Practice creating "junk processes" with sleep &, then use ps to identify their PIDs and kill them using both kill and kill -9.
8. Important Reminders
• Case Sensitivity: Linux is strictly case-sensitive for commands, filenames, and passwords.
• Password Entry: When typing passwords in the terminal, nothing will appear on the screen (no stars or dots) for security reasons. Type carefully and press Enter.

--------------------------------------------------------------------------------