🔹 1. Commonly Used Shell Commands

bashCopyEditls, cp, mv, mkdir, touch, vim, grep, find, df -h

🔹 2. List All Processes

bashCopyEditps -ef

✅ Only Process IDs:

bashCopyEditps -ef | awk '{print $2}'

🔹 3. Extract Errors from Remote Log

bashCopyEditcurl <log_url> | grep -i "error"

📝 Replace <log_url> with actual log file URL (S3, GitHub, etc.)

🔹 4. Print Numbers Divisible by 3 & 5 (but not 15)

bashCopyEditfor i in {1..100}; do
  if (( i % 3 == 0 && i % 5 == 0 && i % 15 != 0 )); then
    echo $i
  fi
done

🔹 5. Count “s” in Mississippi

bashCopyEditecho "Mississippi" | grep -o "s" | wc -l

🔹 6. Debug a Shell Script

bashCopyEditset -x

🔹 7. Crontab (Schedule a Task)

bashCopyEdit0 0 * * * /path/to/script.sh

🕛 Runs daily at midnight.

🔹 8. Open a File in Read-Only Mode

bashCopyEditvim -R test.txt

🔹 9. Difference Between Soft Link & Hard Link

In Linux, links are used to create references to files. There are two types: Soft (Symbolic) Links and Hard Links.

Feature	Hard Link	Soft Link (Symbolic Link)
Points to	Actual data on disk (inode)	File name/path
File deletion	Data stays if original is deleted	Link breaks if original is deleted
Cross-filesystem	❌ Cannot span across filesystems	✅ Can link across filesystems
Directories	❌ Cannot link directories (usually)	✅ Can link directories
Command	`ln source.txt hardlink.txt`	`ln -s source.txt softlink.txt`

📝 In summary:

Hard links are real clones of the original file (same inode).
Soft links are shortcuts — useful but fragile if the source file is removed.🔹 10. break vs continue

Command	Behavior
`break`	Exits the loop
`continue`	Skips current iteration

Example:

bashCopyEditif (( i % 15 == 0 )); then
  continue
fi

🔹 11. Disadvantages of Shell Scripts

While shell scripts are powerful for automation and system-level tasks, they come with several limitations:
1. ❌ Errors are frequent and costly
  - A single typo or wrong character can change the entire command behavior.
2. 🐢 Slow execution speed
  - Scripts are interpreted, not compiled — leading to slower performance.
3. 🐞 Language syntax bugs or limitations
  - Minimal error handling, no robust debugger, and loosely typed variables can cause issues.
4. 🔄 Not ideal for large/complex tasks
  - Shell is best for small tasks. For complex logic or UI, use a more structured language.
5. 📉 Minimal data structures
  - Unlike Python or JavaScript, shell offers only basic variables and arrays.
6. ⚙️ New process for each command
  - Every shell command spawns a new process, which adds overhead and affects performance.

✅ Use shell for: automation, quick scripts, file management.
❌ Avoid for: complex business logic, large-scale applications, data-intensive tasks.

🔹 12. Types of Loops

Loop	Use Case
`for`	Known number of iterations
`while`	Loop while condition true
`until`	Loop until condition true

🔹 13. Is Bash Dynamically Typed?

✅ Yes. No need to declare variable types — just assign and go.

🔹 14. Network Troubleshooting Utilities

bashCopyEdittraceroute google.com
tracepath google.com

🔍 Used to trace the route and diagnose network issues.

🔹 15. Sort Names in a File

bashCopyEditsort names.txt

🔹 16. Manage Huge Log Files (with logrotate)

Example Config:

bashCopyEdit/var/log/myapp.log {
  daily
  rotate 7
  compress
  missingok
}

📦 logrotate compresses and rotates old logs automatically.

✅ Pro Tip: Practice commands and scripts regularly. Mastering small things like grep, awk, and conditionals will make you stand out in interviews.

Shell Scripting & Linux Interview Cheatsheet