Advanced Questions

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Level: Advanced

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1. How do you define a function in Bash?

function_name() {
    # commands
}

Or using the function keyword:

function function_name {
    # commands
}

2. How do you pass arguments to a function?

Just like a script: function_name arg1 arg2.

Inside the function, access them using $1, $2, etc.

3. How do you return a value from a function?

Using return exit_code (0-255) or echo for strings.

• return: Only returns an integer status code (captured by $?).
• echo: Prints output which can be captured via substitution result=$(my_function).

4. What is the scope of variables in a function?

Global by default.

Use the local keyword to make a variable restricted to the function:

local var_name="value"

5. How do you process text using awk?

awk is used for pattern scanning and processing.

Example: Print the first column of a file: awk '{print $1}' file.txt

6. How do you replace text using sed?

sed 's/old/new/g' filename.

• s: Substitute
• g: Global (replace all occurrences)

7. How do you find a line number containing a specific string?

grep -n "string" filename.

8. How do you handle zombie processes using scripts?

Find them using ps aux | grep 'Z' and kill the parent process if necessary.

9. How do you run a script in the background?

Append & at the end.

Example: ./script.sh &.

10. What is nohup?

No Hang Up.

It allows a command to keep running even after you log out: nohup ./script.sh &.

11. How do you schedule a script to run periodically?

Using cron.

Edit crontab with crontab -e and add entry: * * * * * /path/to/script.sh

12. How do you check if a port is open?

nc -zv host port.

Example: nc -zv localhost 80.

13. How do you redirect both stdout and stderr to the same file?

./script.sh > log.txt 2>&1.

14. What is eval command?

It takes arguments and executes them as a command. It creates a "second pass" of parsing.

15. How do you debug scripts with bash -x?

It prints each command before executing it, expanding variables. Useful for tracing logic errors.

16. How do you create a temporary file securely?

mktemp.

Example: temp_file=$(mktemp).

17. How do you parse JSON in shell scripts?

Using jq.

Example: cat data.json | jq '.key'.

18. What is xargs used for?

To build and execute command lines from standard input.

Example: find . -name "*.log" | xargs rm.

19. How do you check if a variable is empty?

if [ -z "$var" ]; then ....

20. How do you get unique lines from a file?

sort filename | uniq.

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