PowerShell script that gets the encoding of the specified file.

##############################################################################
##
## Get-FileEncoding
##
## From Windows PowerShell Cookbook (O'Reilly)
## by Lee Holmes (http://www.leeholmes.com/guide)
##
##############################################################################

<#

.SYNOPSIS

    Gets the encoding of a file

.EXAMPLE

    Get-FileEncoding.ps1 .\UnicodeScript.ps1

    BodyName          : unicodeFFFE
    EncodingName      : Unicode (Big-Endian)
    HeaderName        : unicodeFFFE
    WebName           : unicodeFFFE
    WindowsCodePage   : 1200
    IsBrowserDisplay  : False
    IsBrowserSave     : False
    IsMailNewsDisplay : False
    IsMailNewsSave    : False
    IsSingleByte      : False
    EncoderFallback   : System.Text.EncoderReplacementFallback
    DecoderFallback   : System.Text.DecoderReplacementFallback
    IsReadOnly        : True
    CodePage          : 1201

#>

param(
    ## The path of the file to get the encoding of.
    $Path
)

Set-StrictMode -Version 3

## First, check if the file is binary. That is, if the first
## 5 lines contain any non-printable characters.
$nonPrintable = [char[]] (0..8 + 10..31 + 127 + 129 + 141 + 143 + 144 + 157)
$lines = Get-Content $Path -ErrorAction Ignore -TotalCount 5
$result = @($lines | Where-Object { $_.IndexOfAny($nonPrintable) -ge 0 })
if($result.Count -gt 0)
{
    "Binary"
    return
}

## Next, check if it matches a well-known encoding.

## The hashtable used to store our mapping of encoding bytes to their
## name. For example, "255-254 = Unicode"
$encodings = @{}

## Find all of the encodings understood by the .NET Framework. For each,
## determine the bytes at the start of the file (the preamble) that the .NET
## Framework uses to identify that encoding.
foreach($encoding in [System.Text.Encoding]::GetEncodings())
{
    $preamble = $encoding.GetEncoding().GetPreamble()
    if($preamble)
    {
        $encodingBytes = $preamble -join '-'
        $encodings[$encodingBytes] = $encoding.GetEncoding()
    }
}

## Find out the lengths of all of the preambles.
$encodingLengths = $encodings.Keys | Where-Object { $_ } |
    Foreach-Object { ($_ -split "-").Count }

## Assume the encoding is UTF7 by default
$result = [System.Text.Encoding]::UTF7

## Go through each of the possible preamble lengths, read that many
## bytes from the file, and then see if it matches one of the encodings
## we know about.
foreach($encodingLength in $encodingLengths | Sort -Descending)
{
    $bytes = Get-Content -encoding byte -readcount $encodingLength $path | Select -First 1
    $encoding = $encodings[$bytes -join '-']

    ## If we found an encoding that had the same preamble bytes,
    ## save that output and break.
    if($encoding)
    {
        $result = $encoding
        break
    }
}

## Finally, output the encoding.
$result