如何在Select-String的行首使用正则表达式？

我有以下代码，

Write-Output "$(Get-Content $alerfile | Select-String $(Get-Date (Get-Date).AddDays(-1) -Format $filtdate) -Context 0,1000000)"

我只需要返回行首的字符串，我尝试过：

Write-Output "$(Get-Content $alerfile | Select-String ^$(Get-Date (Get-Date).AddDays(-1) -Format $filtdate) -Context 0,1000000)"

但这不起作用。

As Lee_Dailey commented, you need to remove the Write-Output. Also, you're overdoing it with the date in the pattern.

Next, the Select-String cmdlet also has a -Path parameter, so you don't need Get-Content for this.

I suggest something like this:

# insert the datetime format you need here; this is just an example
$filtdate = 'yyyyMMdd HH:mm:ss'
# get yesterdays date formatted using the $filtdate template above
$refdate  = (Get-Date).AddDays(-1).ToString($filtdate)
# find the string beginning with that formatted date and return the results
Select-String -Path $alerfile -Pattern "^$refdate" -Context 0,1000000