CS-150 – Introduction to Command Line Programming

Unix Family of Operating Systems

• Unix = modular OS; core written in C; resources treated as files
• Key traits: small tools + pipes, hierarchical file system, shell scripting culture
• Major variants: original AT\&T Unix, ext{Linux} (open-source re-implementation), macOS

Shell & CLI Basics

• Shell = interface between user & kernel; common types: CLI (focus) and GUI (ignored here)
• Popular shells: sh, bash (default on most Linux), zsh, csh, ksh, tcsh
• Prompt symbols: \$ (regular user) , # (root)
• Command format: command\ [arg1]\ …\ [argN]

Bash Essentials

• Bash ⊇ sh; extra features, intuitive for beginners, cross-platform (Linux, macOS, Windows via WSL)
• Command-line editing via readline (arrows, \text{Ctrl-A/E/K/Y}, \text{Tab} completion, history)

Commands, Flags & Help

• Coreutils & built-ins coexist; built-ins (e.g. cd, pwd) executed by shell itself
• Flags modify behaviour: short (-l), long (--recursive); often order-independent but placed before file args
• Documentation: man, info, command\ --help

Directory & File Operations

• Navigation: pwd, cd\ dir, cd\ .., cd (home)
• Directories: mkdir (create), rmdir (remove empty)
• Listing: ls with common flags -a\,-l\,-t\,-R
• Files: touch (create/update timestamp), cp (copy), mv (move/rename), rm (remove)
• Viewing: cat (concatenate), head/tail (\text{-n} lines), less (paging), echo (print)

I/O Redirection & Pipes

• File descriptors: stdin 0, stdout 1, stderr 2
• Redirect stdout: > (overwrite), >> (append)
• Redirect stderr: 2> file
• Redirect stdin: < file
• Pipe: command1\ |\ command2 (stdout → stdin)

Wildcards (Globbing)

• * any string; ? single char; [abc] char class/range; {a,b} alternatives

Permissions & Ownership

• Three subjects: user, group, other; three rights: read r, write w, execute x
• Octal mapping: rwx=7, rw-=6, r-x=5, r--=4, etc.
• Change permissions: chmod\ 774\ file (numeric) or chmod\ +x\ file (symbolic)
• Change owner/group: chown\ user{:group}\ file

Shell Scripting Basics

• Script = text file with sequential shell commands; extension .sh (convention)
• Shebang #!\/bin\/bash → selects interpreter
• Creation: any editor (e.g. nano), redirection, etc.
• Execution: source\ script.sh (current shell) or ./script.sh (needs chmod\ +x)

Quick Reference Resources

• learnshell.org – interactive practice
• guide.bash.academy – conceptual deep-dive
• linuxconfig.org & ryanstutorials.net – beginner-friendly tutorials