PowerShell Script to Remove Blank Lines from File

Use Get-Content input.txt | Where-Object { $_.Trim() -ne '' } | Set-Content output.txt to remove blank lines from a file in PowerShell.

Examples

InputLine 1 Line 3 Line 6

OutputLine 1 Line 3 Line 6

Input

Output

InputFirst line Second line Third line

OutputFirst line Second line Third line

How to Think About It

To remove blank lines, read the file line by line, check if each line is not empty or only spaces using Trim(), then keep only those lines and write them back to a file.

Algorithm

1

Read all lines from the input file.

2

For each line, remove spaces from start and end using <code>Trim()</code>.

3

Check if the trimmed line is not empty.

4

Keep lines that are not empty.

5

Write the filtered lines to the output file.

Code

powershell

Get-Content input.txt | Where-Object { $_.Trim() -ne '' } | Set-Content output.txt
Write-Output "Blank lines removed and saved to output.txt"

Output

Blank lines removed and saved to output.txt

Dry Run

Let's trace the input file with lines: 'Line 1', '', 'Line 3', '', '', 'Line 6' through the code.

1

Read lines

["Line 1", "", "Line 3", "", "", "Line 6"]

2

Filter non-blank lines

Keep lines where Trim() is not empty: ["Line 1", "Line 3", "Line 6"]

3

Write output

Write filtered lines to output.txt

Original Line	Trimmed Line	Keep?
Line 1	Line 1	Yes
		No
Line 3	Line 3	Yes
		No
		No
Line 6	Line 6	Yes

Why This Works

Step 1: Read file lines

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

Step 2: Filter blank lines

The Where-Object filters lines where Trim() removes spaces and checks if the line is not empty.

Step 3: Save filtered lines

The filtered lines are saved back to a file using Set-Content.

Alternative Approaches

Using -replace operator

powershell

$content = Get-Content input.txt -Raw
$content -replace '^(\s*\r?\n)+', '' | Set-Content output.txt
Write-Output "Blank lines removed using -replace"

This reads the whole file as one string and removes blank lines with regex; good for small files but uses more memory.

Using ForEach-Object with condition

powershell

Get-Content input.txt | ForEach-Object { if ($_.Trim() -ne '') { $_ } } | Set-Content output.txt
Write-Output "Blank lines removed using ForEach-Object"

Explicitly checks each line and outputs only non-blank lines; slightly more verbose but clear.

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

Time Complexity

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

Space Complexity

All lines are stored in memory during processing, so space grows linearly with file size.

Which Approach is Fastest?

The pipeline with Where-Object is efficient and readable; regex approach uses more memory but can be faster for small files.

Approach	Time	Space	Best For
Where-Object filter	O(n)	O(n)	Large files, readability
-replace regex	O(n)	O(n)	Small files, regex familiarity
ForEach-Object condition	O(n)	O(n)	Explicit control, clarity