Shell

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Curriculum

Coder Merlin™  Computer Science Curriculum Data

Unit: Lab basics Experience Name: Shell (W1002) Next Experience: Help Me! (W1003) Knowledge and skills: §10.121 Demonstrate proficiency in managing files and processes using a command line interface Topic areas: SSH clients; Linux; Bash Classroom time (average): 60 minutes Study time (average): 180 minutes Successful completion requires knowledge: differentiate between a CLI and GUI; understand the purpose of a prompt and cursor; understand files, directories, and their organizational hierarchy; understand processes; understand the client-server model Successful completion requires skills: ability to successfully navigate the file hierarchy; ability to create new, empty files; ability to create new text files; ability to append text to an existing file; ability to move and rename files and directories; ability to delete files and directories; ability to suspend and resume processes; ability to terminate processes; ability to successfully determine your location in the file hierarchy

This is a multi-page experience, consisting of the following pages. Be sure to visit them all in sequence. A navigation bar at the bottom of each page is available to assist you.

• Client and Server
• First Connection
• The Shell
• Terminating a Partial Command
• Directories
• Tab Completion
• Recall Previous Commands
• Alter Previous Commands
• Files
• Deleting a File
• Renaming a File
• Directories Revisited
• Clear the Screen
• Jobs
• Change Your Password
• Display a Manual
• Exiting the Shell

[[Shell/Alter Previous Commands, Shell/Change Your Password, Shell/Clear the Screen, Shell/Client and Server, Shell/Deleting a File, Shell/Directories, Shell/Directories Revisited, Shell/Display a Manual, Shell/Exiting the Shell, Shell/Files, Shell/First Connection, Shell/Jobs, Shell/Recall Previous Commands, Shell/Renaming a File, Shell/Tab Completion, Shell/Terminating a Partial Command, Shell/The Shell<ul><li>"]]" is not a number.</li> <!--br--><li>Some use of "" in your query was not closed by a matching "".</li></ul>|« Prior]]Shell : 1 of 17Next »

Display a Manual

Finally, let's try out one more very helpful command. If we want to learn more about a command we can read its manual. We do this with the command man. As an example, look at the man page for the emacs command. Type man emacs.

john-williams@codermerlin:~/Merlin$  man emacs

The screen will be filled with information about the emacs command. While a man page is displayed we can use the following keys to navigate:

• Typing f will move us forward one page in the manual
• Typing b will move us backward one page in the manual
• Typing q will quit (exit the manual)

Exit the manual now.

Exiting the Shell

In general, there's no need to exit the shell. It's almost always sufficient to close your terminal emulator. An advantage to this approach is that the next time you connect to the server you'll be in exactly the same place where you left off. However, on rare occasions the terminal emulator can become "confused" and display characters in odd places. In such a case, there's still no need to exit; instead, use the reset command.

👀 See Also

📺 Videos

Bash Terminal Beginner's Guide
Linus Torvalds

📖 Texts

Help Me!
Shell

📚 References

• https://en.wikipedia.org/wiki/Operating_system
• https://en.wikipedia.org/wiki/System_software
• https://en.wikipedia.org/wiki/Computer_hardware
• https://en.wikipedia.org/wiki/Application_software
• https://en.wikipedia.org/wiki/Shell_(computing)
• https://en.wikibooks.org/wiki/A_Quick_Introduction_to_Unix/Files_and_Processes
• https://en.wikibooks.org/wiki/A_Quick_Introduction_to_Unix/Directory_Structure
• https://unix.stackexchange.com/questions/89114/what-does-the-jargon-filesystem-mean
• http://www.aboutlinux.info/2005/05/job-control-in-linux.html
• https://www.cis.gvsu.edu/linux-tutorial-job-control/
• https://unix.stackexchange.com/questions/4214/what-is-the-difference-between-a-job-and-a-process

Key Concepts

Key Concepts

• A client-server model is a means of distributing resources between the provider of a service and a consumer of that service, the client. The advantages of this model include:
  • Users don't need to personally possess the hardware and software required to implement the service
  • Users don't need to worry about installation and configuration
  • Users are able to access their data from anywhere in the world
  • The state of a users data remains consistent, regardless of how and from where they access the server
• A shell is a user interface which provides access to an operating system’s services. There are two basic types of shells:
  • A command-line interface (CLI)
  • A graphical user interface (GUI)
• A prompt lets you know that the server is ready and waiting for your input
• A cursor is a flashing block which indicates where new characters will appear as you type
• A file is either a destination or source for a stream of data
• A process is a program that is being executed by the operating system
• All files are integrated into a single, hierarchical structure called a directory
  • A directory provides a logical grouping of related files (and potentially other directories)
  • The top of this tree is called the root and is referred to by a slash (/)
  • A subdirectory is a directory contained within another directory, called the parent directory
  • On Unix systems, the file structure is logical rather than physical
  • A path describes an ordered transition through one or more directories on the way to a destination (either a directory or a file)
    • Paths which begin at the root (symbolized by the initial slash) are called absolute paths
    • All other paths are relative paths
  • Your home directory is indicated by a special symbol, the tilde (~)
  • Your working directory can be thought of as your current directory
  • The command pwd prints the working directory
  • The command mkdir creates a new directory
  • The command ls lists the contents of a directory
  • The command cd changes your working directory
  • The command pushd changes our working directory temporarily
  • The command popd returns us to our previous directory after executing pushd
  • The command tree displays a directory hierarchy
  • The command rmdir removes (deletes) a directory
• The echo command echoes the argument to the output
• The touch command creates a new, empty file, if such a file does not already exist. If such a file does already exist, the access and modification times will be set to the current time.
• The greater-than symbol (>) can be used to redirect output to a file
• Two greater-than symbols (>>) can be used to append output to a file
• The cat command allows us to quickly view the contents of one or more files
• The rm command is used to remove (delete) a file
• The mv command is used to either move or rename a file
• The clear command clears the screen
• A program is an executable file which contains a series of instructions which can be executed by the computer
• A process is a program which is being executed on the computer
• The shell manages processes using jobs
• The jobs command will list the current jobs associated with your shell
  • A job can be terminated by using the key sequence CONTROL-C
  • A job can be suspended by using the key sequence CONTROL-Z
  • A job can be resumed in the foreground with fg
  • A job can be resumed in the background with bg
• The man command displays the contents of a manual
• The reset command resets your terminal

Exercises

Exercises

Using pencil and paper, answer all questions in this experience.

---

After completing W1005:

•  J1002  Create a journal and answer all questions in this experience. Be sure to include all sections of the journal, properly formatted.

---

After completing W1008:

•  M1002-10  Complete  Merlin Mission Manager  Mission M1002-10.
•  M1002-31  Verify your journal's conformance with  Merlin Mission Manager  Mission M1002-31.

Experience Metadata

Edit Experience Metadata

Experience ID	W1002
Next experience ID
Unit	Lab basics
Knowledge and skills	§10.121
Topic areas	SSH clients Linux Bash
Classroom time	1 hour60 minutes <br />
Study time	3 hours180 minutes <br />
Acquired knowledge	differentiate between a CLI and GUI understand files, directories, and their organizational hierarchy understand of the client-server model understand processes understand the purpose of a prompt and cursor
Acquired skill	ability to append text to an existing file ability to create new text files ability to create new, empty files ability to delete files and directories ability to move and rename files and directories ability to successfully determine location in the file hierarchy ability to successfully navigate the file hierarchy ability to suspend and resume processes ability to terminate processes
Additional categories