Linux Bash

Expert guidance for Linux bash operations, scripting, and system administration.

Core Commands

File Operations

• ls -lah – List files with details, including hidden
• find /path -name "pattern" – Find files by name
• grep -r "pattern" /path – Recursive text search
• chmod +x file – Make file executable
• chown user:group file – Change ownership
• tar -czf archive.tar.gz dir/ – Create compressed archive
• tar -xzf archive.tar.gz – Extract archive

Process Management

• ps aux | grep process – Find running processes
• top / htop – Monitor system resources
• kill -9 PID – Force kill process
• nohup command & – Run command in background
• jobs – List background jobs
• fg %1 – Bring job to foreground

System Information

• df -h – Disk usage human-readable
• du -sh dir/ – Directory size
• free -h – Memory usage
• uname -a – System information
• lsb_release -a – Distribution info

Text Processing

• cat file | head -n 10 – First 10 lines
• tail -f log.txt – Follow log file
• sed 's/old/new/g' file – Replace text
• awk '{print $1}' file – Print first column
• sort file | uniq – Remove duplicates

Shell Scripting Best Practices

Script Template

#!/bin/bash
set -euo pipefail  # Exit on error, undefined vars, pipe failures

# Script description
readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

main() {
    # Your logic here
    echo "Hello, World!"
}

main "$@"

Error Handling

# Check command success
if ! command -v tool &> /dev/null; then
    echo "Error: tool not found" >&2
    exit 1
fi

# Trap errors
trap 'echo "Error on line $LINENO"' ERR

Variables

# Constants (uppercase)
readonly CONFIG_FILE="/etc/app.conf"

# Variables (lowercase)
user_input="$1"

# Arrays
files=("file1.txt" "file2.txt")
for file in "${files[@]}"; do
    echo "$file"
done

Common Patterns

Check if file exists

if [[ -f "file.txt" ]]; then
    echo "File exists"
fi

Loop through files

for file in *.txt; do
    echo "Processing $file"
done

Read user input

read -p "Enter value: " user_value

Function definition

my_function() {
    local arg1="$1"
    echo "Received: $arg1"
}

Tips

1. Quote variables: Always use "$variable" to prevent word splitting
2. Use [[ ]] for tests: More features than [ ]
3. Shellcheck: Use shellcheck script.sh to validate scripts
4. Exit codes: Use $? to check last command status
5. Debugging: Use set -x to trace execution

Safety First

• Always test scripts in safe environment first
• Use set -e to exit on errors
• Validate input parameters
• Quote file paths to handle spaces
• Use absolute paths when possible