Get names of script parameters

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This function parses parameters of a script and returns parameter names. For example, I use it in my own TabExpansion procedure. It requires PowerShell 2.0.

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function GetScriptParameter
(
    # Full script path.
    $Path,
    # Script code (if $Path is not defined).
    $Script,
    # Parameter wildcard pattern (to get a subset).
    $Pattern
)
{
    if ($Path) {
        $Script = [System.IO.File]::ReadAllText($Path)
    }

    $mode = 0
    $param = $true
    $tokens = @([System.Management.Automation.PSParser]::Tokenize($Script, [ref]$null))
    for($i = 0; $i -lt $tokens.Count; ++$i) {
        $t = $tokens[$i]

        # skip [ whatever ]
        if (($t.Type -eq 'Operator') -and ($t.Content -eq '[')) {
            $level = 1
            for(++$i; $i -lt $tokens.Count; ++$i) {
                $t = $tokens[$i]
                if ($t.Type -eq 'Operator') {
                    if ($t.Content -eq '[') {
                        ++$level
                    }
                    elseif($t.Content -eq ']') {
                        --$level
                        if ($level -le 0) {
                            break
                        }
                    }
                }
            }
            continue
        }

        switch($t.Type) {
            'NewLine' { break }
            'Comment' { break }
            'Command' {
                if ($mode -le 1) {
                    return
                }
                break
            }
            'Keyword' {
                if ($mode -eq 0) {
                    if ($t.Content -eq 'param') {
                        $mode = 1
                        break
                    }
                }
            }
            'GroupStart' {
                if ($mode) {
                    ++$mode
                    break
                }
                else {
                    return
                }
            }
            'GroupEnd' {
                --$mode
                if ($mode -lt 2) {
                    return
                }
            }
            'Variable' {
                if ($mode -eq 2 -and $param) {
                    $param = $false
                    if ((!$Pattern) -or ($t.Content -like $Pattern)) {
                        $t.Content
                    }
                    break
                }
            }
            'Operator' {
                if (($mode -eq 2) -and ($t.Content -eq ',')) {
                    $param = $true
                }
            }
        }
    }
}

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