shell

## What I do - Use shell commands effectively - Write robust shell scripts - Manage processes and jobs - Handle I/O redirection and pipes - Automate tasks - Debug shell scripts ## When to use me When working in terminal, automating tasks, or writing shell scripts. ## Shell Types - **bash**: Bourne Again Shell, most popular - **zsh**: Z Shell, Oh My Zsh, advanced features - **fish**: Friendly Interactive Shell, user-friendly - **sh**: POSIX shell, portable ## Basic Commands ### File Operations ```bash ls -la # List with details cp -r # Copy recursive rm -rf # Force remove mkdir -p # Create nested dirs chmod # Change permissions chown # Change owner ``` ### Text Processing ```bash cat # View file grep # Search pattern sed # Stream editor awk # Text processing sort # Sort lines uniq # Unique lines head/tail # First/last lines wc # Word count ``` ### System ```bash ps # Process status top/htop # Process monitor kill # Kill process df # Disk free du # Disk usage free # Memory ``` ## Scripting ### Shebang ```bash #!/bin/bash #!/usr/bin/env bash ``` ### Variables ```bash NAME="John" echo $NAME echo ${NAME} # Arrays arr=(one two three) echo ${arr[0]} ``` ### Conditionals ```bash if [ $name = "admin" ]; then echo "Hello admin" elif [ $name = "guest" ]; then echo "Hello guest" else echo "Hello stranger" fi ``` ### Loops ```bash # For loop for f in *.txt; do echo "Processing $f" done # While loop while read line; do echo "$line" done < file.txt ``` ### Functions ```bash greet() { local name=$1 echo "Hello, $name" } greet "World" ``` ## Advanced Features ### I/O Redirection ```bash > # Redirect stdout 2> # Redirect stderr &> # Redirect both >> # Append < # Redirect stdin | # Pipe ``` ### Process Substitution ```bash diff <(ls dir1) <(ls dir2) ``` ### Parameter Expansion ```bash ${var:-default} # Default if unset ${var:=default} # Set default ${var:?error} # Error if unset ${var#pattern} # Remove prefix ${var%pattern} # Remove suffix ${var/old/new} # Replace ``` ### Globbing ```bash *.txt # All txt files file?.txt # file1.txt, file2.txt [abc]*.txt # Starting with a,b,c ``` ## Best Practices - Use `set -euo pipefail` - Quote variables - Use `[[ ]]` over `[ ]` - Add comments - Use functions - Check exit codes - Use shellcheck - Make scripts portable