Top 50 Shell Script Interview Question and Answers

Top 50 Shell Script Interview Question and Answers

1. What is a shell script?

A shell script is a program written for the shell, or command line interpreter, of an operating system. It consists of a series of commands to be executed by the shell.

2. How do you execute a shell script?

You can execute a shell script by making it executable with chmod +x scriptname.sh and then running it with ./scriptname.sh.

3. What is the default shell in Linux?

The default shell in most Linux distributions is Bash (Bourne Again Shell).

4. How do you create a variable in a shell script?

Variables are created by assigning values using the = operator, e.g., VAR=value.

5. How do you read user input in a shell script?

You can read user input using the read command, e.g., read input.

6. How do you create a function in a shell script?

Functions are defined using the syntax:

function_name() {

commands

}

comma

7. What are positional parameters in a shell script?

Positional parameters are used to pass arguments to a script and are accessed using $1, $2, etc.

8. How do you check if a file exists in a shell script?

Use the -e option with an if statement, e.g., [ -e filename ].

9. How do you compare two numbers in a shell script?

Use the -eq, -ne, -lt, -le, -gt, and -ge operators, e.g., [ $a -eq $b ].

10. What is the purpose of #!/bin/bash at the beginning of a script?

This is a shebang line that tells the system which interpreter to use to execute the script.

11. How do you make a script executable?

Use the chmod +x scriptname.sh command.

12. How do you create an infinite loop in a shell script?

Use while true; do commands; done.

13. How do you write comments in a shell script?

Use the # symbol to write comments.

14. What does the echo command do?

echo is used to display a message or the value of a variable.

15. How do you check if a directory exists in a shell script?

Use the -d option, e.g., [ -d dirname ].

16. How do you append output to a file in a shell script?

Use the » operator, e.g., echo “text” » file.txt.

17. How do you redirect stderr to a file in a shell script?

Use 2>, e.g., command 2> errorfile.

18. What is the difference between == and = in shell scripting?

= is used for assignment, while == is used for comparison in test commands.

19. How do you perform arithmetic operations in a shell script?

Use $(()), e.g., result=$((a + b)).

20. What is the use of the set command?

set is used to set or unset shell options and positional parameters.

21. How do you exit a script and return a value to the caller?

Use the exit command followed by a number, e.g., exit 0.

22. What are shell script’s special variables?

$0 (script name), $# (number of arguments), $@ (all arguments), $? (exit status of last command).

23. How do you declare an array in a shell script?

Use array=(element1 element2 element3).

24. How do you access array elements in a shell script?

Use ${array[index]}.

25. What is the IFS variable?

IFS (Internal Field Separator) defines the character used for word splitting.

26. How do you execute a command and store its output in a variable?

Use backticks or $(command), e.g., output=$(ls).

27. What is the purpose of the trap command?

trap is used to catch signals and execute commands when the signal is received.

28. How do you use a for loop in a shell script?

Syntax:

for var in list; do

commands

done

comman

29. How do you use a case statement in a shell script?

Syntax:

case $variable in

pattern1)

commands ;;

pattern2)

commands ;;

esac

30. What is the difference between > and »?

overwrites a file, while » appends to a file.

31. How do you check the exit status of a command?

Use $? to get the exit status of the last command executed.

32. What is the use of the exec command?

exec replaces the current shell with a specified command.

33. How do you use the find command in a shell script?

Example: find /path -name filename.

34. How do you pass arguments to a shell script?

Arguments are passed as positional parameters, accessed using $1, $2, etc.

35. What is a here document?

A here document allows you to redirect multiple lines of input into a command, using the « delimiter.

36. How do you handle errors in a shell script?

Check the exit status of commands and use conditional statements to handle errors.

37. What is the use of the sleep command?

sleep pauses the execution for a specified amount of time.

38. How do you find the length of a string in a shell script?

Use ${#string}.

39. How do you substring a string in a shell script?

Use ${string:position:length}.

40. How do you replace a substring in a string in a shell script?

Use ${string//search/replace}.

41. How do you check if a string is empty in a shell script?

Use [ -z “$string” ].

42. How do you concatenate strings in a shell script?

Use string1=$string1$string2.

43. What is the use of the basename command?

basename removes the directory part of a path and returns the filename.

44. How do you check if a command exists in a shell script?

Use command -v commandname or which commandname.

1. What is the cut command used for?

cut is used to remove sections from each line of files.

46. How do you use the awk command in a shell script?

awk is a pattern scanning and processing language. Example: awk ‘{print $1}’ file.

47. How do you use the sed command in a shell script?

sed is a stream editor. Example: sed ‘s/old/new/’ file.

48. How do you use the grep command in a shell script?

grep searches for patterns in files. Example: grep “pattern” file.

49. What is a pipeline in shell scripting?

50. How do you use logical AND and OR in shell scripting?