PowerShell Script to Count Lines in a File

Use (Get-Content filename.txt).Count in PowerShell to count the number of lines in a file.

Examples

Inputfile content: "Hello\nWorld"

Output2

Inputfile content: "Line1\nLine2\nLine3"

Output3

Inputfile content: "" (empty file)

Output0

How to Think About It

To count lines in a file, read all lines into memory and then count how many lines were read. PowerShell's Get-Content reads the file line by line into an array, and counting the array elements gives the line count.

Algorithm

1

Get the file path as input.

2

Read all lines from the file into a list.

3

Count the number of lines in the list.

4

Output the count.

Code

powershell

param([string]$filePath = "sample.txt")

if (Test-Path $filePath) {
    $lineCount = (Get-Content $filePath).Count
    Write-Output "Number of lines: $lineCount"
} else {
    Write-Output "File not found: $filePath"
}

Output

Number of lines: 3

Dry Run

Let's trace counting lines in a file with 3 lines: 'Line1', 'Line2', 'Line3'.

1

Check if file exists

File 'sample.txt' exists.

2

Read file lines

Get-Content reads lines: ['Line1', 'Line2', 'Line3']

3

Count lines

Count is 3.

Step	Action	Value
1	File exists?	True
2	Lines read	['Line1', 'Line2', 'Line3']
3	Line count	3

Why This Works

Step 1: Reading the file

The Get-Content command reads the file line by line into an array.

Step 2: Counting lines

Using .Count on the array returns how many lines were read.

Step 3: Outputting result

The script prints the total line count to the console.

Alternative Approaches

Using Measure-Object

powershell

$lineCount = Get-Content sample.txt | Measure-Object -Line | Select-Object -ExpandProperty Lines
Write-Output "Number of lines: $lineCount"

This method streams the file and counts lines without loading all lines into memory at once, better for large files.

Using .NET StreamReader

powershell

$count = 0
$reader = [System.IO.StreamReader]::new('sample.txt')
while ($reader.ReadLine() -ne $null) { $count++ }
$reader.Close()
Write-Output "Number of lines: $count"

This approach reads the file line by line manually, useful for very large files to reduce memory usage.

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

Time Complexity

The script reads each line once, so time grows linearly with the number of lines.

Space Complexity

Using Get-Content loads all lines into memory, so space grows with file size.

Which Approach is Fastest?

Using Measure-Object streams lines and uses less memory, making it faster for large files.

Approach	Time	Space	Best For
Get-Content with .Count	O(n)	O(n)	Small to medium files
Get-Content with Measure-Object	O(n)	O(1)	Large files
.NET StreamReader loop	O(n)	O(1)	Very large files with minimal memory