如何在PowerShell中的第一个特殊字符实例后删除数组中每行中的剩余文本

Question

I would like to remove the remaining text in each line of an array, including and after the first instance of a period character (ie '.'). This is the code I'm using but I'm getting this error: Exception calling "Substring" with "2" argument(s): "Length cannot be less than zero. Parameter name: length"

    $Textfile = Get-Content "C:\Temp\Text.txt"

    $Textfile | Foreach {
    $Textfile.Substring(1,$Textfile.IndexOf('.'))
    }
    $Textfile | Out-File C:\Temp\Text2.txt

Answer 1

Try something like this:

Get-Content myfile.txt | foreach {@($_ -split '\.')[0]}

Notes:

1. The foreach processes the file one line at a time (but you knew that).
2. The @ forces the result to be an array, even if there is only one string, in case no dots.
3. The $_ references the current line of the file.
4. The backslash before the dot is an escape character in Regex
5. The [0] selects the first item from the array.

Answer 2

Inside your Foreach loop, you need to work on the current item, $_ instead of the entire $Textfile array.

Should probably be something like this:

$Textfile | Foreach {
    $_.Substring(1,$Textfile.IndexOf('.'))
} | Out-File C:\Temp\Text2.txt

Please note that you may still get the same error if it comes across a line without a '.'

Answer 3

Try the next approach:

$Textfile|Foreach {$_ -replace '(^[^.]*)(.*)','$1'}|Out-File C:\Temp\Text2.txt

... or other:

$Textfile|
Foreach {if(($p=$_.indexof('.')) -ge 0){$_.substring(0,$p)}else{$_}}|
Out-File C:\Temp\Text2.txt

Answer 4

The problem I see is that your $TextFile variable holds the entire contents of the file, but you call substring on the index of period in the entire contents of the file. Also, you call substring from 1, not 0. So after the second call, you'll be guaranteed to receive that error. My attempts to correct it below.

$Textfile = Get-Content "C:\Temp\Text.txt"

$NewFileContents = @($Textfile | Foreach {
    if ($_.IndexOf(".") -eq -1)
    {
        $_
    }
    else
    {
        $_.Substring(0,$_.IndexOf('.'))
    }
}) -Join "`r`n"

$NewFileContents | Out-File C:\Temp\Text2.txt

More code explanation: String indexing begins at 0, not 1. In other words, the first character is 0. When you called $FileContents.Substring(1), you were eliminating the first character each time. Since you also called it on the variable $FileContents each time, and not on the line of the new file, it consistently got shorter. Using the anonymous variable that comes from the foreach loop ($_), you get the contents of each line.

I call ($ .IndexOf(".") -eq -1) to verify if there exists a period on the line. By checking if there exists a period on each line before doing the substring, we remove the possibility of saying $ .Substring(0,-1) which would give unpredictable results.