function - 如何正确调用Powershell函数？

Question

我编写了一个函数，将输入的month参数转换为某种格式。例如我将04传递给该函数，该函数将返回“ _ APR_”。我写的功能如下:

function GetEnMonth()
{
param([string] $month)
switch ($month)
{
    ($_ -eq "01"){$result = "_JAN_"}
    ($_ -eq "02"){$result = "_FEB_"}
    ($_ -eq "03"){$result = "_MAR_"}
    ($_ -eq "04"){$result = "_APR_"}
    ($_ -eq "05"){$result = "_MAY_"}
    ($_ -eq "06"){$result = "_JUN_"}
    ($_ -eq "07"){$result = "_JUL_"}
    ($_ -eq "08"){$result = "_AUG_"}
    ($_ -eq "09"){$result = "_SEP_"}
    ($_ -eq "10"){$result = "_OCT_"}
    ($_ -eq "11"){$result = "_NOV_"}
    ($_ -eq "12"){$result = "_DEC_"}
    default {$result ="_No_Result_"}
}
return [string]$result;
} 

然后，我使用以下命令执行该函数以获取结果:

$mYear = $today.substring(0,4) 
$mMonth =$today.substring(4,2)
$mDate = $today.substring(6,2)
$monthInEn = GetEnMonth $mMonth

好吧，结果总是“_No_Result_”，为什么呢？以下是异常(exception):

 **** Exception type : System.Management.Automation.RuntimeException
 **** Exception message : You cannot call a method on a null-valued expression.

有人可以给我答案吗？
我已经搜索了很多Google，但是找不到有用的解决方案。

Answer 1

您的switch语句错误，请尝试以下操作:

function GetEnMonth()
{
param([string] $month)
switch ($month)
{
    "01" {$result = "_JAN_"}
    "02" {$result = "_FEB_"}
    "03" {$result = "_MAR_"}
    "04" {$result = "_APR_"}
    "05" {$result = "_MAY_"}
    "06" {$result = "_JUN_"}
    "07" {$result = "_JUL_"}
    "08" {$result = "_AUG_"}
    "09" {$result = "_SEP_"}
    "10" {$result = "_OCT_"}
    "11" {$result = "_NOV_"}
    "12" {$result = "_DEC_"}
    default {$result ="_No_Result_"}
}
return [string]$result;
}