Weird PowerShell Exec Output Capture Behavior

Question

I'm writing a simple PowerShell script that handles the output of mkvinfo. It captures the output of mkvinfo, stores in a variable $s and does some post-processing on $s. The strange part is while $s has content, I can't extract a substring from it.

The error message I'm getting was:

Exception calling "Substring" with "1" argument(s): "startIndex cannot be larger than length of string. Parameter name: startIndex"

This is a sample code:

$filePath = $folder + $file.name
$mkvinfoExe = "C:\mkvinfo.exe"
$s = & $mkvinfoExe $filePath
$s | out-host
$s.Substring($s.Length-1) | out-host

manojlds · Accepted Answer · 2012-11-10 10:40:38Z

4

Are you sure $s is a string and not an array? If it is an array, $s.Length will be the number of elements in the array and you could get the error that you are getting.

For example:

PS > $str = @("this", "is", "a")
PS > $str.SubString($str.Length - 1)
Exception calling "Substring" with "1" argument(s): "startIndex cannot be larger than length of string.
Parameter name: startIndex"
At line:1 char:1
+ $str.SubString($str.Length - 1)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : ArgumentOutOfRangeException

answered Nov 10, 2012 at 10:40

manojlds

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1 Comment

Jim Over a year ago

Ha I realized it just a few seconds before your answer. Will accept answer in 5 minutes. Thanks!

Jim · Accepted Answer · 2012-11-10 10:40:46Z

1

Just found out because mkvinfo outputs multiple lines, $s is actually a String array (or List?). Switching to $s[0].Substring($s[0].Length-1) solves it.

answered Nov 10, 2012 at 10:40

Jim

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