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

• Quote variables: Always use "$variable" to prevent word splitting

• Use [[ ]] for tests: More features than [ ]

• Shellcheck: Use shellcheck script.sh to validate scripts

• Exit codes: Use $? to check last command status

• 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