Recursive functions in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple recursive factorial function

What is the output of this Bash script when run?

Bash Scripting

#!/bin/bash
factorial() {
  if [ "$1" -le 1 ]; then
    echo 1
  else
    local prev=$(factorial $(( $1 - 1 )))
    echo $(( $1 * prev ))
  fi
}
factorial 5

A 120

B 24

C Error: command not found

D 1

💡 Hint

Think about how factorial is defined and how recursion multiplies numbers down to 1.

The function calls itself with decreasing values until it reaches 1, then multiplies back up: 5*4*3*2*1 = 120.

💻 Command Output

intermediate

Output of recursive Fibonacci function

What does this Bash script print when executed?

Bash Scripting

#!/bin/bash
fib() {
  if [ "$1" -le 1 ]; then
    echo $1
  else
    local a=$(fib $(( $1 - 1 )))
    local b=$(fib $(( $1 - 2 )))
    echo $(( a + b ))
  fi
}
fib 6

A Error: maximum recursion depth exceeded

B 13

C 5

D 8

💡 Hint

Remember the Fibonacci sequence starts 0,1,1,2,3,5,8...

fib(6) = fib(5) + fib(4) = 5 + 3 = 8.

📝 Syntax

advanced

Identify the syntax error in this recursive function

Which option correctly identifies the syntax error in this Bash recursive function?

Bash Scripting

#!/bin/bash
countdown() {
  if [ $1 -le 0 ]
    echo "Done!"
  else
    echo "$1"
    countdown $(( $1 - 1 ))
  fi
}
countdown 3

A Using echo inside recursion is not allowed

B Incorrect use of $(( )) for arithmetic

C Missing 'then' after the if condition

D Missing closing brace '}' for the function

💡 Hint

Check the if statement syntax carefully.

In Bash, an if statement must have 'then' after the condition. It's missing here.

🚀 Application

advanced

What is the output of this recursive directory listing script?

Given this Bash script that recursively lists files, what will it output when run in a directory with files 'a.txt' and subdirectory 'sub' containing 'b.txt'?

Bash Scripting

#!/bin/bash
list_files() {
  for item in "$1"/*; do
    if [ -d "$item" ]; then
      list_files "$item"
    else
      echo "$item"
    fi
  done
}
list_files "."

A

./a.txt
./sub/b.txt

B

a.txt
b.txt

C

./sub
./a.txt
./sub/b.txt

D Error: infinite recursion

💡 Hint

The script prints file paths, not directories.

The script prints only files, recursively descending into directories. It prints './a.txt' and './sub/b.txt'.

🔧 Debug

expert

Why does this recursive function cause a stack overflow?

Examine this Bash recursive function. Why does it cause a stack overflow when called with 3?

Bash Scripting

#!/bin/bash
infinite() {
  echo "$1"
  infinite $1
}
infinite 3

A The arithmetic expansion is missing in the recursive call

B The function calls itself with the same argument, causing infinite recursion

C Bash does not support recursion

D The function lacks a base case to stop recursion

💡 Hint

Think about what stops recursion normally.

The function calls itself with the same argument endlessly, no base case to stop it, causing stack overflow.