Bash Script to Reverse Words in a String

Use echo "$string" | awk '{for(i=NF;i>0;i--) printf "%s%s", $i, (i==1?"\n":" ")}' to reverse words in a string in Bash.

Examples

Inputhello world

Outputworld hello

InputBash scripting is fun

Outputfun is scripting Bash

Input

Output

How to Think About It

To reverse words in a string, think of splitting the string into separate words, then printing them starting from the last word to the first, joining them back with spaces.

Algorithm

1

Get the input string.

2

Split the string into words based on spaces.

3

Start from the last word and move to the first word.

4

Print each word followed by a space except the last one.

5

Return the reversed word string.

Code

bash

read -r string
reversed=$(echo "$string" | awk '{for(i=NF;i>0;i--) printf "%s%s", $i, (i==1?"\n":" ")}')
echo "$reversed"

Output

world hello

Dry Run

Let's trace the input 'hello world' through the code

1

Input string

string = 'hello world'

2

Split into words

words = ['hello', 'world']

3

Print words in reverse

output = 'world hello'

Iteration	Word Printed	Output So Far
1	world	world
2	hello	world hello

Why This Works

Step 1: Splitting the string

The awk command splits the input string into fields (words) automatically.

Step 2: Looping backwards

The for loop runs from the last word (NF) to the first (1), reversing the order.

Step 3: Printing words

Each word is printed with a space except the last one, which ends with a newline for clean output.

Alternative Approaches

Using Bash arrays

bash

read -r string
read -ra words <<< "$string"
for (( idx=${#words[@]}-1; idx>=0; idx-- )); do
  printf "%s" "${words[idx]}"
  [[ $idx -ne 0 ]] && printf " "
done
printf "\n"

This uses Bash arrays and a loop, which is pure Bash but slightly longer.

Using rev and tac with process substitution

bash

read -r string
echo "$string" | tr ' ' '\n' | tac | tr '\n' ' '
echo

This converts words to lines, reverses lines, then joins back, but adds a trailing space before newline.

Complexity: O(n) time, O(n) space

Time Complexity

The script processes each word once in a loop, so time grows linearly with the number of words.

Space Complexity

It stores all words temporarily, so space grows linearly with input size.

Which Approach is Fastest?

The awk one-liner is efficient and concise; Bash arrays are readable but slightly longer; using tac involves extra process calls.

Approach	Time	Space	Best For
awk one-liner	O(n)	O(n)	Concise and fast for most cases
Bash arrays	O(n)	O(n)	Pure Bash, easy to understand
tac with tr	O(n)	O(n)	When you prefer pipeline commands