Why PowerShell Removes Newlines in Expandable Strings and How to Fix It

When you use expandable strings in PowerShell like "$(command)", the command output loses its original line breaks because PowerShell treats the output as an array of strings and joins them with spaces rather than preserving newlines. This happens because the $OFS (Output Field Separator) variable defaults to a space, causing PowerShell to join array elements with spaces when they’re embedded in a double-quoted string.

Contents

• Understanding the Root Cause
• Methods to Preserve Newlines
  • Using the -join Operator
  • Assigning to Variables First
  • Using Here-Strings
  • Working with File Content
• Advanced Techniques
• Best Practices

Understanding the Root Cause

When you execute a command like hledger accounts --directive --types in PowerShell, it returns an array of strings where each element represents a line from the original output. When you embed this command in an expandable string:

"$(hledger accounts --directive --types)"

PowerShell performs these steps:

1. Executes the command
2. Captures the output as an array of strings
3. Joins the array elements using the $OFS variable (which defaults to a space)
4. Places the result in the double-quoted string

This process converts your multi-line output into a single string with spaces where newlines should be. The newline characters ("n") are treated as whitespace and get collapsed during the joining process.

Methods to Preserve Newlines

Using the -join Operator

The most direct solution is to explicitly join the command output with newline characters:

"$(hledger accounts --directive --types -join "`n")"

This tells PowerShell to join the array elements with actual newline characters instead of spaces. The -join operator takes precedence over the automatic joining that occurs in expandable strings.

You can also use this approach when working with variables:

$accounts = hledger accounts --directive --types
"Account list:`n$($accounts -join "`n")"

Assigning to Variables First

Assigning the command output to a variable first often preserves the newlines when referenced in a string:

$accounts = hledger accounts --directive --types
"This is my accounts list:`n$accounts"

When you reference a variable containing an array in a double-quoted string, PowerShell automatically preserves the elements’ original formatting, including newlines.

Using Here-Strings

For more complex scenarios, here-strings preserve all whitespace including newlines:

@"
Hledger Accounts:
$(hledger accounts --directive --types)
End of list
"@

Here-strings maintain their formatting exactly as written, making them ideal for multi-line output.

Working with File Content

If your command output is being saved to or read from a file, use Get-Content with the -Raw parameter:

# Save the command output to a file first
hledger accounts --directive --types | Out-File -FilePath "accounts.txt"

# Read it back with -Raw to preserve newlines
$content = Get-Content -Path "accounts.txt" -Raw
$content

The -Raw parameter reads the entire file as a single string rather than splitting it into lines.

Advanced Techniques

For more complex formatting needs, you can combine multiple techniques:

# Process each line individually
$processedAccounts = hledger accounts --directive --types | ForEach-Object {
    # Add some formatting to each line
    "[$_]"
}

# Join with newlines
$result = $processedAccounts -join "`n"

# Use in a larger string
@"
Processed Accounts:
$result
"@

You can also normalize different line endings that might cause inconsistent display:

# Normalize different line endings to Unix-style newlines
$normalizedOutput = (hledger accounts --directive --types) -replace "`r`n", "`n" -replace "`r", "`n"
$normalizedOutput

Best Practices

1. Test with small outputs first: Always verify your approach works with a limited subset of data before applying it to large outputs.

2. **Be aware of $OFS**: Remember that modifying `$OFS` will affect how array elements join in double-quoted strings:

   powershell

   # Temporarily change the separator
   $originalOFS = $OFS
   $OFS = "`n"
   "Array: $(@('line1', 'line2', 'line3'))"
   $OFS = $originalOFS
   

3. Handle special characters: If your output contains special characters or escape sequences, use proper escaping:

   powershell

   $escaped = $output -replace '`', '``' -replace '$', '`$'
   

4. Consider the display context: If you’re displaying output directly to the console, you might not need to preserve newlines in a string. Sometimes executing the command directly is better:

   powershell

   # Instead of:
   Write-Host "$(hledger accounts --directive --types -join "`n")"
   
   # Just use:
   hledger accounts --directive --types
   

By applying these techniques, you can reliably preserve newlines when using command output in PowerShell expandable strings, ensuring your output maintains its intended formatting regardless of how it’s embedded in larger strings.