Bash Commands & Scripting

 1#!/bin/bash
 2
 3# Command dispatcher script
 4command_dispatcher() {
 5    local cmd="$1"
 6    shift  # Remove first argument, rest are parameters
 7    
 8    case "$cmd" in
 9        start)
10            echo "Starting service..."
11            # Your start logic here
12            ;;
13        stop)
14            echo "Stopping service..."
15            # Your stop logic here
16            ;;
17        restart)
18            stop
19            start
20            ;;
21        status)
22            echo "Checking status..."
23            # Your status logic here
24            ;;
25        deploy)
26            local env="$1"
27            echo "Deploying to $env..."
28            # Your deploy logic here
29            ;;
30        *)
31            echo "Usage: $0 {start|stop|restart|status|deploy <env>}"
32            exit 1
33            ;;
34    esac
35}
36
37# Call dispatcher with all arguments
38command_dispatcher "$@"

 1# Find files modified in last 7 days
 2find . -type f -mtime -7
 3
 4# Find and delete files older than 30 days
 5find . -type f -mtime +30 -delete
 6
 7# Find files by size (larger than 100MB)
 8find . -type f -size +100M
 9
10# Find and replace in files
11find . -type f -name "*.txt" -exec sed -i 's/old/new/g' {} +
12
13# Copy with progress
14rsync -ah --progress source/ destination/
15
16# Create directory structure
17mkdir -p path/to/nested/directories
18
19# Disk usage sorted by size
20du -sh * | sort -h
21
22# Find largest files
23find . -type f -exec du -h {} + | sort -rh | head -n 10

 1# Extract column from CSV
 2cut -d',' -f2 file.csv
 3
 4# Count lines/words/chars
 5wc -l file.txt
 6
 7# Remove duplicate lines
 8sort file.txt | uniq
 9
10# Count unique lines
11sort file.txt | uniq -c
12
13# Get lines between patterns
14sed -n '/START/,/END/p' file.txt
15
16# Replace text in-place
17sed -i 's/old/new/g' file.txt
18
19# Print specific lines
20sed -n '10,20p' file.txt
21
22# AWK: sum column
23awk '{sum+=$1} END {print sum}' file.txt
24
25# AWK: print if condition
26awk '$3 > 100' file.txt
27
28# Join lines
29paste -sd',' file.txt

 1# Find process by name
 2ps aux | grep process_name
 3
 4# Kill process by name
 5pkill process_name
 6
 7# Kill process by port
 8lsof -ti:8080 | xargs kill -9
 9
10# Run in background
11command &
12
13# Run and detach from terminal
14nohup command &
15
16# Check if process is running
17pgrep -x process_name > /dev/null && echo "Running" || echo "Not running"
18
19# Monitor process
20watch -n 1 'ps aux | grep process_name'

 1# Check port is open
 2nc -zv hostname 80
 3
 4# Download file
 5curl -O https://example.com/file.zip
 6
 7# POST JSON data
 8curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' https://api.example.com
 9
10# Check HTTP status
11curl -I https://example.com
12
13# Test DNS
14dig example.com
15
16# Show listening ports
17netstat -tuln
18
19# Show network connections
20ss -tuln

 1# CPU info
 2lscpu
 3
 4# Memory info
 5free -h
 6
 7# Disk space
 8df -h
 9
10# System uptime
11uptime
12
13# Kernel version
14uname -r
15
16# Distribution info
17cat /etc/os-release
18
19# List loaded modules
20lsmod
21
22# Hardware info
23lshw -short

 1#!/bin/bash
 2set -euo pipefail  # Exit on error, undefined var, pipe failure
 3
 4# Trap errors
 5trap 'echo "Error on line $LINENO"' ERR
 6
 7# Check command success
 8if ! command -v git &> /dev/null; then
 9    echo "git not found"
10    exit 1
11fi

 1#!/bin/bash
 2
 3# Parse options
 4while getopts "hf:v" opt; do
 5    case $opt in
 6        h)
 7            echo "Usage: $0 [-h] [-f file] [-v]"
 8            exit 0
 9            ;;
10        f)
11            file="$OPTARG"
12            ;;
13        v)
14            verbose=true
15            ;;
16        \?)
17            echo "Invalid option: -$OPTARG" >&2
18            exit 1
19            ;;
20    esac
21done
22
23# Shift past options
24shift $((OPTIND-1))
25
26# Remaining arguments
27echo "Remaining args: $@"

 1#!/bin/bash
 2
 3# Function with return value
 4get_timestamp() {
 5    date +%Y%m%d_%H%M%S
 6}
 7
 8# Function with parameters
 9backup_file() {
10    local file="$1"
11    local backup_dir="$2"
12    
13    if [[ ! -f "$file" ]]; then
14        echo "Error: File not found" >&2
15        return 1
16    fi
17    
18    cp "$file" "$backup_dir/$(basename "$file").$(get_timestamp)"
19}
20
21# Usage
22backup_file "/path/to/file.txt" "/backup"

 1# Declare array
 2files=("file1.txt" "file2.txt" "file3.txt")
 3
 4# Iterate array
 5for file in "${files[@]}"; do
 6    echo "$file"
 7done
 8
 9# Array length
10echo "${#files[@]}"
11
12# Add to array
13files+=("file4.txt")
14
15# Associative array (dictionary)
16declare -A config
17config[host]="localhost"
18config[port]="8080"
19
20echo "${config[host]}"

 1# String length
 2str="hello"
 3echo "${#str}"
 4
 5# Substring
 6echo "${str:0:2}"  # "he"
 7
 8# Replace
 9echo "${str/l/L}"  # "heLlo"
10
11# Replace all
12echo "${str//l/L}"  # "heLLo"
13
14# Remove prefix
15path="/usr/local/bin"
16echo "${path#/usr/}"  # "local/bin"
17
18# Remove suffix
19file="document.txt"
20echo "${file%.txt}"  # "document"
21
22# Convert to uppercase
23echo "${str^^}"
24
25# Convert to lowercase
26echo "${str,,}"

 1# File tests
 2if [[ -f "file.txt" ]]; then
 3    echo "File exists"
 4fi
 5
 6if [[ -d "directory" ]]; then
 7    echo "Directory exists"
 8fi
 9
10if [[ -x "script.sh" ]]; then
11    echo "File is executable"
12fi
13
14# String tests
15if [[ -z "$var" ]]; then
16    echo "Variable is empty"
17fi
18
19if [[ "$str1" == "$str2" ]]; then
20    echo "Strings match"
21fi
22
23# Numeric tests
24if [[ $num -gt 10 ]]; then
25    echo "Greater than 10"
26fi
27
28# Logical operators
29if [[ -f "file.txt" && -r "file.txt" ]]; then
30    echo "File exists and is readable"
31fi

 1# For loop
 2for i in {1..10}; do
 3    echo "$i"
 4done
 5
 6# C-style for loop
 7for ((i=0; i<10; i++)); do
 8    echo "$i"
 9done
10
11# While loop
12while read line; do
13    echo "$line"
14done < file.txt
15
16# Until loop
17count=0
18until [[ $count -eq 5 ]]; do
19    echo "$count"
20    ((count++))
21done

 1# Multi-line string
 2cat << EOF > config.txt
 3server {
 4    listen 80;
 5    server_name example.com;
 6}
 7EOF
 8
 9# Here string
10grep "pattern" <<< "string to search"

 1# Backup with timestamp
 2cp file.txt file.txt.$(date +%Y%m%d_%H%M%S)
 3
 4# Find and archive
 5tar czf archive.tar.gz $(find . -name "*.log")
 6
 7# Monitor log file
 8tail -f /var/log/syslog | grep --line-buffered "ERROR"
 9
10# Parallel execution
11cat urls.txt | xargs -P 10 -I {} curl -O {}
12
13# Generate random string
14openssl rand -base64 32
15
16# Check if script is run as root
17[[ $EUID -ne 0 ]] && echo "Must run as root" && exit 1
18
19# Create backup and restore functions
20alias backup='tar czf backup-$(date +%Y%m%d).tar.gz'
21alias restore='tar xzf'