ps/Modules/Cole.PowerShell.Developer/Public/Set-PathVariable.ps1

function Set-PathVariable {
    param (
        [Parameter(Mandatory = $true)]
        [Alias("Store")]
        [Alias("Location")]
        [ValidateSet("Process","User","Machine","Any")]
        [string]$StoreName,
        [Parameter(Mandatory = $false)]
        [string[]]$Append,
        [Parameter(Mandatory = $false)]
        [string[]]$Prepend,
        [Parameter(Mandatory = $false)]
        [string[]]$Remove,
        [string]$PathSeparator = [IO.Path]::PathSeparator
    )

    $processPath = @()
    $userPath = @()
    $machinePath = @()
    $processPathAny = $false
    $userPathAny = $false
    $machinePathAny = $false
    $processPathDirty = $false
    $userPathDirty = $false
    $machinePathDirty = $false

    $modifyAny = $StoreName -eq 'Any'

    if (Any $Remove) {
        $Remove = $Remove.Where({![string]::IsNullOrWhiteSpace($PSItem)})
    }

    if (Any $Prepend) {
        $Prepend = $Prepend.Where({![string]::IsNullOrWhiteSpace($PSItem)})
    }

    if (Any $Append) {
        $Append = $Append.Where({![string]::IsNullOrWhiteSpace($PSItem)})
    }

    if (!(Any $Remove)) {
        $Remove = @()
    }

    $count = 0

    # if we are prepending or appending any paths, yoink them from their existing place
    if (Any $Prepend) {
        $count = $Prepend.Count
        foreach ($prependPath in $Prepend) {
            if ($Remove -notcontains $prependPath) {
                $Remove += $prependPath
            }
        }
    }

    if (Any $Append) {
        # Can't both prepend and append entries.
        # Assume prepend wins
        for ($i=0;$i -lt $count; $i++) {
            $removeIfFound = $Prepend[$i]
            $at = $Append.IndexOf($removeIfFound)
            if ($at -gt -1) {
                $Append.RemoveAt($at)
            }
        }
        foreach ($appendPath in $Append) {
            if ($Remove -notcontains $appendPath) {
                $Remove += $appendPath
            }
        }
    }

    if (!(Any $Remove)) {
        Write-Warning "No paths provided to modify. Exiting with no action taken."
        return
    }

    if (('Process','Any') -contains $StoreName) {
        $processPath = (Get-EnvironmentVariable -Name Path -StoreName 'Process') -split $PathSeparator
        $processPathAny = (Any $processPath)

        # If we were told to modify the process variable but none exists, we should still modify it
        if (!$processPathAny -and !$modifyAny) {
            $processPath = @()
            $processPathAny = $true
        }

        if ($processPathAny) {
            # coerce so we can RemoveAt
            [System.Collections.ArrayList]$processPath = [System.Collections.ArrayList]$processPath
        }
    }

    if (('User','Any') -contains $StoreName) {
        $userPath = (Get-EnvironmentVariable -Name Path -StoreName 'User') -split $PathSeparator
        $userPathAny = (Any $userPath)

        # If we were told to modify the user variable but none exists, we should still modify it
        if (!$userPathAny -and !$modifyAny) {
            $userPath = @()
            $userPathAny = $true
        }

        if ($userPathAny) {
            # coerce so we can RemoveAt
            [System.Collections.ArrayList]$userPath = [System.Collections.ArrayList]$userPath
        }
    }

    if (('Machine','Any') -contains $StoreName) {
        $machinePath = (Get-EnvironmentVariable -Name Path -StoreName 'Machine') -split $PathSeparator
        $machinePathAny = (Any $machinePath)

        # If we were told to modify the machine variable but none exists, we should still modify it
        if (!$machinePathAny -and !$modifyAny) {
            $machinePath = @()
            $machinePathAny = $true
        }

        if ($machinePathAny) {
            # coerce so we can RemoveAt
            [System.Collections.ArrayList]$machinePath = [System.Collections.ArrayList]$machinePath
        }
    }

    $count = $Remove.Count

    # remove first
    if (Any $Remove) {
        if ($processPathAny) {
            for ($i=0;$i -lt $count; $i++) {
                $removeIfFound = $Remove[$i]
                $at = $processPath.IndexOf($removeIfFound)
                if ($at -gt -1) {
                    $processPath.RemoveAt($at)
                    $processPathDirty = $true
                }
            }
        }
        if ($userPathAny) {
            for ($i=0;$i -lt $count; $i++) {
                $removeIfFound = $Remove[$i]
                $at = $userPath.IndexOf($removeIfFound)
                if ($at -gt -1) {
                    $userPath.RemoveAt($at)
                    $userPathDirty = $true
                }
            }
        }
        if ($machinePathAny) {
            for ($i=0;$i -lt $count; $i++) {
                $removeIfFound = $Remove[$i]
                $at = $machinePath.IndexOf($removeIfFound)
                if ($at -gt -1) {
                    $machinePath.RemoveAt($at)
                    $machinePathDirty = $true
                }
            }
        }
    }

    # then append
    if (Any $Append) {
        if ($processPathAny) {
            foreach($appendPath in $Append) {
                if ($processPath -notcontains $appendPath) {
                    $processPath.Add($appendPath)
                }
            }
            $processPathDirty = $true
        }
        if ($userPathAny) {
            foreach($appendPath in $Append) {
                if ($userPath -notcontains $appendPath) {
                    $userPath.Add($appendPath)
                }
            }
            $userPathDirty = $true
        }
        if ($machinePathAny) {
            foreach($appendPath in $Append) {
                if ($machinePath -notcontains $appendPath) {
                    $machinePath.Add($appendPath)
                }
            }
            $machinePathDirty = $true
        }
    }

    # then prepend
    if (Any $Prepend) {
        if ($processPathAny) {
            $processPath = $Prepend + $processPath
            $processPathDirty = $true
        }
        if ($userPathAny) {
            $userPath = $Prepend + $userPath
            $userPathDirty = $true
        }
        if ($machinePathAny) {
            $machinePath = $Prepend + $machinePath
            $machinePathDirty = $true
        }
    }

    # ensure we don't write bad paths by checking for .Where({![string]::IsNullOrWhiteSpace($PSItem)})

    if ($processPathDirty) {
        Set-EnvironmentVariable -Name Path -Value ($processPath.Where({![string]::IsNullOrWhiteSpace($PSItem)}) -join $PathSeparator) -StoreName 'Process'
    }

    if ($userPathDirty) {
        Set-EnvironmentVariable -Name Path -Value ($userPath.Where({![string]::IsNullOrWhiteSpace($PSItem)}) -join $PathSeparator) -StoreName 'User'
    }

    if ($machinePathDirty) {
        Set-EnvironmentVariable -Name Path -Value ($machinePath.Where({![string]::IsNullOrWhiteSpace($PSItem)}) -join $PathSeparator) -StoreName 'Machine'
    }
}