bash

## What I do - Write automation scripts for system tasks - Process and transform data files - Manage processes and system resources - Create interactive shell menus - Parse logs and configuration files - Handle error conditions and debugging - Manage text processing with grep, sed, awk - Schedule jobs with cron and at - Create reusable script functions - Build complex workflows ## When to use me When automating system administration tasks, processing data files, creating shell scripts, or working in Linux/Unix environments. ## Core Concepts - Bash scripting syntax and best practices - Parameter expansion and quoting - Process substitution and pipes - Control structures (if, case, loops, functions) - Regular expressions with grep/sed/awk - Exit codes and error handling - Arrays and associative arrays - Here-documents and here-strings - Signal handling and traps - Subshells and command grouping ## Code Examples ### System Automation Scripts ```bash #!/usr/bin/env bash set -euo pipefail # Configuration readonly LOG_FILE="/var/log/backup.log" readonly BACKUP_DIR="/backup" readonly RETENTION_DAYS=30 # Logging function log() { local level="$1" shift local message="$@" echo "[$(date '+%Y-%m-%d %H:%M:%S')] [$level] $message" | tee -a "$LOG_FILE" } # Database backup function backup_postgresql() { local db_name="$1" local timestamp=$(date +%Y%m%d_%H%M%S) local backup_file="${BACKUP_DIR}/${db_name}_${timestamp}.sql.gz" log "INFO" "Starting backup of database: $db_name" if pg_dump "$db_name" | gzip > "$backup_file"; then local size=$(du -h "$backup_file" | cut -f1) log "INFO" "Backup completed: $backup_file ($size)" # Verify backup integrity if gzip -t "$backup_file" 2>/dev/null; then log "INFO" "Backup verified successfully" else log "ERROR" "Backup verification failed!" return 1 fi else log "ERROR" "Backup failed for database: $db_name" return 1 fi } # Cleanup old backups cleanup_old_backups() { log "INFO" "Cleaning up backups older than $RETENTION_DAYS days" local deleted=0 while IFS= read -r -d '' file; do rm -f "$file" ((deleted++)) log "INFO" "Removed: $file" done < <(find "$BACKUP_DIR" -name "*.sql.gz" -mtime +$RETENTION_DAYS -print0) log "INFO" "Cleaned up $deleted old backup files" } # Health check function health_check() { local checks_passed=0 local checks_failed=0 # Check disk space if df / | awk 'NR==2 {exit ($5 > 90)}'; then log "INFO" "Disk space check: PASSED" ((checks_passed++)) else log "ERROR" "Disk space check: FAILED (>/= 90% used)" ((checks_failed++)) fi # Check memory local mem_usage=$(free | awk '/Mem:/ {printf "%.0f", $3/$2 * 100}') if (( $(echo "$mem_usage < 90" | bc -l) )); then log "INFO" "Memory check: PASSED ($mem_usage%)" ((checks_passed++)) else log "ERROR" "Memory check: FAILED ($mem_usage%)" ((checks_failed++)) fi # Check critical services for service in nginx postgresql redis; do if systemctl is-active --quiet "$service"; then log "INFO" "Service $service: RUNNING" ((checks_passed++)) else log "ERROR" "Service $service: NOT RUNNING" ((checks_failed++)) fi done log "INFO" "Health check complete: $checks_passed passed, $checks_failed failed" return $checks_failed } # Main execution main() { log "INFO" "=========================================" log "INFO" "Backup script started" # Run health check first health_check || { log "WARN" "Health check failed, but continuing with backup" } # Backup databases for db in app_production app_staging; do backup_postgresql "$db" || log "ERROR" "Failed to backup: $db" done # Cleanup old backups cleanup_old_backups log "INFO" "Backup script completed" log "INFO" "=========================================" } # Execute main function main "$@" ``` ### Advanced Data Processing ```bash #!/usr/bin/env bash set -euo pipefail # Parse CSV and generate reports generate_user_report() { local csv_file="$1" local output_dir="$2" # Create output directory mkdir -p "$output_dir" # Process CSV with awk awk -F',' ' NR > 1 { # Count by department dept_count[$3]++ # Sum salaries dept_salary[$3] += $5 # Track active/inactive if ($6 == "active") active_count++ else inactive_count++ } END { print "Department Report" print "=================" for (dept in dept_count) { printf "%-20s: %3d employees, $%10.2f avg salary\n", \ dept, dept_count[dept], dept_salary[dept] / dept_count[dept] } printf "\nTotal Active: %d\nTotal Inactive: %d\n", active_count, inactive_count }' "$csv_file" > "$output_dir/department_summary.txt" # Generate JSON with jq-like approach using Python python3 <<PYEOF import csv import json import sys data = [] with open('$csv_file', 'r') as f: reader = csv.DictReader(f) for row in reader: data.append({ 'id': int(row['id']), 'name': row['name'], 'email': row['email'], 'department': row['department'], 'salary': float(row['salary']) }) with open('$output_dir/users.json', 'w') as f: json.dump(data, f, indent=2) PYEOF log "INFO" "Reports generated in $output_dir" } # Concurrent processing with GNU parallel process_files_concurrent() { local source_dir="$1" local dest_dir="$2" local max_jobs="${3:-4}" export DEST_DIR="$dest_dir" process_single_file() { local file="$1" local basename=$(basename "$file") echo "Processing $basename to $DEST_DIR" # Actual processing logic here cp "$file" "$DEST_DIR/${basename%.txt}_processed.txt" } export -f process_single_file find "$source_dir" -name "*.txt" -print0 | \ xargs -0 -P "$max_jobs" -I {} bash -c 'process_single_file "$@"' _ {} } ``` ### Network Utilities ```bash #!/usr/bin/env bash # Port scanner scan_ports() { local host="${1:-localhost}" local start_port="${2:-1}" local end_port="${3:-1024}" echo "Scanning $host ports $start_port-$end_port..." for port in $(seq $start_port $end_port); do if timeout 0.5 bash -c "echo > /dev/tcp/$host/$port" 2>/dev/null; then echo "Port $port: OPEN ($(grep "^$port/" /etc/services 2>/dev/null | cut -f1 || echo 'unknown')" fi done } # Network bandwidth monitor monitor_bandwidth() { local interface="${1:-eth0}" local interval="${2:-1}" echo "Monitoring $interface bandwidth (interval: ${interval}s)" echo "RX (MB) TX (MB) RX/s TX/s" echo "------- ------- ------ ------" local prev_rx=$(cat /sys/class/net/$interface/statistics/rx_bytes) local prev_tx=$(cat /sys/class/net/$interface/statistics/tx_bytes) while true; do sleep "$interval" local curr_rx=$(cat /sys/class/net/$interface/statistics/rx_bytes) local curr_tx=$(cat /sys/class/net/$interface/statistics/tx_bytes) local rx_diff=$((curr_rx - prev_rx)) local tx_diff=$((curr_tx - prev_tx)) printf "%7.2f %7.2f %7.2f %7.2f\n" \ $((curr_rx / 1024 / 1024)) $((curr_tx / 1024 / 1024)) \ $(echo "scale=2; $rx_diff / 1024 / 1024 / $interval" | bc) \ $(echo "scale=2; $tx_diff / 1024 / 1024 / $interval" | bc) prev_rx=$curr_rx prev_tx=$curr_tx done } ``` ## Best Practices - Always use `set -euo pipefail` at script start - Use double quotes around variables to prevent word splitting - Use `readonly` for constants and configuration values - Prefer `printf` over `echo` for portable output - Use functions to organize code and enable testing - Return meaningful exit codes (0=success, non-zero=failure) - Document scripts with comments and usage functions - Handle signals with trap for cleanup - Avoid parsing output of `ls` - use globs instead - Test scripts with shellcheck for common issues