PowerShell：如何间接引用变量

Question

在 Powershell 中，如何间接引用变量？

我有在代码的许多部分中引用的表，所以我有一个表名列表，如下所示：

$xTableName = "Tbl_x"
$yTableName = "Tbl_y"
$zTableName = "Tbl_z"

我有一个函数，我想将一个表示表格的字符串传递给它：

function getResult($entityName)
{
$tableName="$" + $entityName + "TableName"
$sqlCommand = "SELECT * FROM " + ${$tableName}
run query etc...
}

我打电话

getResult("x")

我正在尝试获取 $sqlCommand = "SELECT * FROM Tbl_x" 但获取的是 "SELECT * FROM $xTableName"

我如何做到这一点？

Answer 1

您可以使用Get-Variable -ValueOnly 按名称获取变量的值：

$tableName = Get-Variable "${entityName}TableName" -ValueOnly

话虽如此，更快且不易出错的方法是利用字典将实体名称映射到表名称：

function getResult($entityName)
{
    $tableMapping = @{
        x = "Tbl_x"
        y = "Tbl_y"
        z = "Tbl_z"
    }
    if(-not $tableMapping.ContainsKey($entityName)){
        Write-Error "Invalid entity name '$entityName'"
    }
    else {
        $tableName = $tableMapping[$entityName]
        $sqlCommand = "SELECT * FROM ${$tableName}"
        # execute sql query ...
    }
}

Answer 2

更简洁的方法是使用正则表达式。我们可以这样做：

$xTableName = "Tbl_x"
$yTableName = "Tbl_y"
$zTableName = "Tbl_z"

function getResult($TableName)
{
    $sqlCommand = "SELECT * FROM tableName" -creplace "tableName","$TableName"
}
getResult($xTableName)