powershell-regex-matches-safety

name	powershell-regex-matches-safety
description	Protect parsed values from later -match operations by copying PowerShell $Matches groups into local variables immediately.
domain	powershell
confidence	high
source	earned

powershell-regex-matches-safety

When to Use

• A function parses content with -match and then loops over lines with more -match calls.
• You need the original capture groups later in the function.

Pattern

1. Run the outer regex match once.
2. Copy every needed capture group from $Matches into local variables immediately.
3. Use those local variables after any later -match operations.

Why

PowerShell reuses the ambient $Matches variable for every successful -match. If you keep reading $Matches after a loop that performs more regex matches, later matches can silently overwrite the original capture groups.

Example

if ($content -match '(?ms)^---\s*\r?\n(.*?)\r?\n---\s*\r?\n?(.*)$') {
    $frontmatterBlock = [string]$Matches[1]
    $bodyContent = [string]$Matches[2]

    foreach ($line in ($frontmatterBlock -split '\r?\n')) {
        if ($line -match '^\s*([^:]+):\s*(.*?)\s*$') {
            # Later matches do not clobber $bodyContent
        }
    }
}