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Understanding Unix/Linux Shell: Basics, Commands, and File Management

The Unix/Linux shell serves as an essential interface between users and the kernel, enabling command input and script execution. This guide covers various shell types (Bourne, C-shell), essential commands (like `man`, `ls`, `chmod`), and file systems organization. Learn about file types, directory navigation, environment variables, and managing input/output. Key concepts include process management and redirection techniques. This resource is perfect for both new and experienced users looking to master their command-line interactions on Unix/Linux systems.

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Understanding Unix/Linux Shell: Basics, Commands, and File Management

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  1. Unix/Linux cs3353

  2. The Shell • The shell is a program that acts as the interface between the user and the kernel. • The shell is fully programmable and will interpret lists of commands entered by the user, or read cmds from a file (known as a script). • A prompt is displayed by the shell program indicating it is ready to accept input from the user.

  3. Shell Types • Bourne Shell (ALGOL syntax) • sh, • bash • ksh • zsh • C-shell (based on C language syntax) • csh • tcsh

  4. Unix/Linux Commands • commandName options files • man commandName • to read about the command Example: man find

  5. accounts • Root • Has absolute control over the OS • Regular • User login id number, string, and password.

  6. Shell Startup • The .bash_profile (in place of the .profile) and .bashrc are used at TU. • Ubuntu, .bashrc

  7. Linux Files • Everything in the OS is organized into files. • There is a i-node for every file on the file system (i = information)

  8. Files • Regular files includes (aka ordinary) • executable (*) and • hidden files (.). • Special files: • Symbolic link (@) • Directory (d) • Others: block special, named pipe, character special Use the cmd: file filename Use the ls command.

  9. The File System • Navigate with cd, pwd, ls • Organized by directories • mkdir, rmdir • cp, mv, rm • / is known as root • /boot • /home • /var • /tmp

  10. Directory Pathnames • Absolute – always begins with root /. • Relative – does not begin with root ./aFile bFile /home/user/cFile ../data/dFile

  11. File names • See pg 57 • 255 characters, no / allowed.

  12. ls –l • Type-user-group-other • -rwxr-xr— • Token 1 • Token 2-4 • Token 5-7 • Token 8-10 • Access control is through the chmod cmd.

  13. chmod • Octal: • chmod [ugo]+|-[rwx] • Octal r=4, w=2, x=1, the complement of umask • X is required for a script to run (pg 29) • Examples

  14. The Shell Env • Variables • Local are only visible in the current process. • Environment variables are inherited by sub-processes, Example: PATH • PATH is used by the shell to find commands entered by the user. export PATH=$PATH:.:~/bin echo $PATH

  15. Input and Output • STDIN = 0 the standard input • STDOUT = 1 the standard output • STDERR = 2 the standard error • Most cmds are designed to display output to the stdout • Many cmds are designed to read input from the stdin. • Error messages go to stderr.

  16. Input & Output • The default location for output is the terminal screen. • It is possible to redirect the output of a command to: • Another command using a pipe | • A file using the output redirect symbol > Example: date > aFile ps | wc –l

  17. Input & Output • It is possible to control the input to a command • The read command is designed to capture input from the standard input: cat << stop > file >Steve >stop greeting < file echo “What is your name?” read Name echo “Greetings $Name”

  18. Processes • Init is process id # 1 • Dummy processes during system startup do not have a process ID. • All other processes have a process ID.

  19. Example • Use ps and sleep to introduce background processes using the & • ps will show processes running on a system. • A process can be stopped (killed) by using the PID. kill pid

  20. Substitution (Meta Characters) • *, ?, [range] • !, ^, $

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