PowerShell: How to limit string to N characters?

substring complains when I try to limit a string to 10 characters which is not 10 or more characters in length. I know I can test the length but I would like to know if there is a single cmdlet which will do what I need.

PS C:\> "12345".substring(0,5)
12345

PS C:\> "12345".substring(0,10)
Exception calling "Substring" with "2" argument(s): "Index and length must refer to a location within the string.
Parameter name: length"
At line:1 char:18
+ "12345".substring( 开发者_如何学Python<<<< 0,10)

Do you need exactly a cmdlet? I wonder why you don't like getting length. If it's part of a script, then it looks fine.

$s = "12345"
$s.substring(0, [System.Math]::Min(10, $s.Length))

Using the substring function has it's limitations and requires you to first capture the length of the string. Granted this does work you can do it without that limitation.

The following will return the first 5 characters of the string

"1234567890"[0..4] -join ""     # returns the string '12345'

And this will work on strings that are shorter than desired length

"1234567890"[0..1000] -join ""  # returns the string '1234567890'

You can load and use other libraries and use their string functions, for example the visual basic string functions work nicely for what you want to do

call once per session >[void][reflection.assembly]::LoadWithPartialName("microsoft.visualbasic")

then use various vb string functions

>[microsoft.visualbasic.strings]::left("12345",10)
12345

or

>[microsoft.visualbasic.strings]::mid("12345",1,10)
12345

The previous answers didn't suit my purposes (no offence!) so I took Denomales suggestion above and rolled it into a function which I thought I'd share:

function Trim-Length {
param (
    [parameter(Mandatory=$True,ValueFromPipeline=$True)] [string] $Str
  , [parameter(Mandatory=$True,Position=1)] [int] $Length
)
    $Str[0..($Length-1)] -join ""
}

Example usages:

"1234567" | Trim-Length 4    # returns: "1234"
"1234" | Trim-Length 99      # returns: "1234"

Thanks to Dmitry for the answer, I turned it into a function and made it so it is 1 based as opposed to 0 based.

function acme-substr ([string]$str, $start, $end) {
   $str.substring($start-1, [System.Math]::Min($str.Length-1, $end))
}

> $foo="0"*20
> $foo
00000000000000000000
> acme-substr $foo 1 5
00000