PowerShell Script to Capitalize First Letter of a String

Use $str = $str.Substring(0,1).ToUpper() + $str.Substring(1) to capitalize the first letter of a string in PowerShell.

Examples

Inputhello

OutputHello

InputpowerShell

OutputPowerShell

Inputa

OutputA

How to Think About It

To capitalize the first letter, take the first character of the string and convert it to uppercase, then add the rest of the string unchanged. This keeps the original string except for the first letter.

Algorithm

1

Get the input string.

2

Extract the first character and convert it to uppercase.

3

Extract the rest of the string starting from the second character.

4

Combine the uppercase first character with the rest of the string.

5

Return or print the new string.

Code

powershell

$str = "hello"
$str = $str.Substring(0,1).ToUpper() + $str.Substring(1)
Write-Output $str

Output

Hello

Dry Run

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

1

Original string

$str = 'hello'

2

First letter uppercase

$str.Substring(0,1).ToUpper() = 'H'

3

Rest of string

$str.Substring(1) = 'ello'

4

Combine parts

'H' + 'ello' = 'Hello'

Step	Value
Original string	hello
First letter uppercase	H
Rest of string	ello
Combined result	Hello

Why This Works

Step 1: Extract first character

Using Substring(0,1) gets the first letter of the string.

Step 2: Convert to uppercase

Calling ToUpper() changes the first letter to uppercase.

Step 3: Add the rest

The rest of the string is added unchanged using Substring(1).

Alternative Approaches

Using -replace with regex

powershell

$str = 'hello'
$str = $str -replace '^(.)', { $args[0].Value.ToUpper() }
Write-Output $str

Uses regex to replace the first character with its uppercase version; slightly more complex but flexible.

Using char array and manual change

powershell

$str = 'hello'
$chars = $str.ToCharArray()
$chars[0] = [char]::ToUpper($chars[0])
$str = -join $chars
Write-Output $str

Converts string to array, changes first char, then joins back; useful if you want to manipulate characters individually.

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

Time Complexity

The operation processes the string parts once, so it runs in linear time relative to string length.

Space Complexity

A new string is created combining parts, so space grows linearly with input size.

Which Approach is Fastest?

The substring method is straightforward and efficient; regex adds overhead but offers flexibility.

Approach	Time	Space	Best For
Substring + ToUpper	O(n)	O(n)	Simple and fast capitalization
Regex Replace	O(n)	O(n)	Flexible pattern matching
Char Array Manipulation	O(n)	O(n)	Character-level control