Bash Script to Capitalize First Letter of Each Word

Use echo "$string" | awk '{for(i=1;i<=NF;i++) $i=toupper(substr($i,1,1)) substr($i,2)}1' to capitalize the first letter of each word in Bash.

Examples

Inputhello world

OutputHello World

Inputbash scripting is fun

OutputBash Scripting Is Fun

Input123 easy as abc

Output123 Easy As Abc

How to Think About It

To capitalize the first letter of each word, split the input string into words, then for each word, change the first character to uppercase and keep the rest as is. Finally, join the words back together.

Algorithm

1

Get the input string.

2

Split the string into words by spaces.

3

For each word, convert the first letter to uppercase and keep the rest unchanged.

4

Combine all words back into a single string.

5

Output the transformed string.

Code

bash

read -r input
output=$(echo "$input" | awk '{for(i=1;i<=NF;i++) $i=toupper(substr($i,1,1)) substr($i,2)}1')
echo "$output"

Output

Hello World

Dry Run

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

1

Input read

input = 'hello world'

2

Process each word

Word 1: 'hello' -> 'H' + 'ello' = 'Hello' Word 2: 'world' -> 'W' + 'orld' = 'World'

3

Output combined

Output = 'Hello World'

Word	Original	First Letter Uppercase	Result
1	hello	H	Hello
2	world	W	World

Why This Works

Step 1: Splitting words

The awk command splits the input string into words using spaces.

Step 2: Capitalizing first letter

For each word, toupper(substr($i,1,1)) converts the first character to uppercase.

Step 3: Rebuilding words

The rest of the word is appended unchanged using substr($i,2), then all words are printed.

Alternative Approaches

Using Bash parameter expansion

bash

read -r input
for word in $input; do
  printf '%s ' "${word^}"
done
echo

Simple and pure Bash, but splits on spaces only and may not handle punctuation well.

Using sed with regex

bash

read -r input
echo "$input" | sed -E 's/(^| )[a-z]/\U&/g'

Uses sed to capitalize letters after spaces or start, but may be less readable.

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

Time Complexity

The script processes each word once, so time grows linearly with input length.

Space Complexity

Extra space is used to store the output string, proportional to input size.

Which Approach is Fastest?

Bash parameter expansion is fastest for simple inputs; awk is more robust but slightly slower.

Approach	Time	Space	Best For
awk command	O(n)	O(n)	Robust word capitalization
Bash parameter expansion	O(n)	O(n)	Simple scripts with space-separated words
sed regex	O(n)	O(n)	Quick inline substitutions with regex