bash

## What I do - Write bash scripts for automation - Process text with awk and sed - Use find and xargs effectively - Handle command-line arguments - Manage environment variables - Implement error handling - Create utility functions ## When to use me When automating tasks, building CLI tools, or managing systems. ## Basics ```bash #!/bin/bash # Variables name="World" echo "Hello, $name!" # Command substitution current_date=$(date +%Y-%m-%d) files=$(ls) # Arrays colors=("red" "green" "blue") echo "${colors[0]}" echo "${colors[@]}" # Dictionaries (bash 4+) declare -A config config[host]="localhost" config[port]="8080" echo "${config[host]}" ``` ## Conditionals ```bash # If statement if [ "$name" == "admin" ]; then echo "Welcome admin" elif [ "$age" -ge 18 ]; then echo "Adult" else echo "Minor" fi # File tests if [ -f "$file" ]; then echo "Regular file" fi if [ -d "$dir" ]; then echo "Directory" fi if [ -z "$var" ]; then echo "Empty" fi # String comparison if [[ "$str" == *"pattern"* ]]; then echo "Contains pattern" fi ``` ## Loops ```bash # For loop for i in {1..5}; do echo "Number: $i" done for file in *.txt; do echo "Processing $file" done # While loop while read line; do echo "$line" done < file.txt # Iterate over array for color in "${colors[@]}"; do echo "$color" done ``` ## Functions ```bash function greet() { local name="$1" # local variable echo "Hello, $name!" } greet "World" # Return value function get_sum() { local a=$1 local b=$2 echo $((a + b)) } result=$(get_sum 5 10) ``` ## Arguments ```bash #!/bin/bash # $@ = all arguments # $# = argument count # $0 = script name # $1, $2, ... = arguments while [[ $# -gt 0 ]]; do case $1 in -h|--help) help=true ;; -n|--name) name="$2" shift 2 ;; -v|--verbose) verbose=true shift ;; *) echo "Unknown: $1" shift ;; esac done ``` ## Error Handling ```bash set -e # Exit on error set -u # Exit on undefined variable set -o pipefail # Pipeline fails on error # Trap errors trap 'echo "Error on line $LINENO"' ERR # Check command success if ! command -v git &> /dev/null; then echo "Git not found" exit 1 fi ``` ## Text Processing ```bash # Awk awk -F',' '{print $1, $3}' file.csv awk 'NR>1 {sum+=$2} END {print sum}' file.txt # Sed sed 's/old/new/g' file.txt sed -i 's/old/new/g' file.txt # in-place sed '/pattern/d' file.txt # delete lines with pattern # Find find . -name "*.txt" -type f find . -mtime -7 # modified in last 7 days find . -size +1M # larger than 1MB # xargs find . -name "*.log" -type f | xargs rm find . -name "*.txt" | xargs -I {} mv {} ./backup/ ``` ## Useful Patterns ```bash # Check if command exists command -v docker >/dev/null 2>&1 || { echo "Docker required"; exit 1; } # Heredoc cat << EOF > config.txt name=$name value=$value EOF # Parallel execution cat hosts | xargs -P 10 -I {} ssh {} 'uptime' # Progress bar for i in {1..100}; do echo -ne "Progress: $i%\r" sleep 0.1 done ```