How to convert hexadecimal encoded string to hexadecimal integer

Question

So basically what I'm trying to achieve is to get a MAC address from a text file and increment the value by one.

Been bashing my head against the Google/StackOverflow wall for a couple of hours, think there's a concept I'm just not getting.

PowerShell:

$Last_MAC_Address = (Get-Content -LiteralPath "\\UNC\Path\Last MAC Address.txt")

Write-Host ($Last_MAC_Address)
# Output: 00155DE10B73

$Next_MAC_Address = (($Last_MAC_Address | Format-Hex) + 1)

([Int64]::Parse('00155DE10B73', 'HexNumber') + 1).ToString('X12') — user4003407
– user4003407, Commented Jul 9, 2016 at 8:07
Decimal: ("Good to know." | Format-Hex).Bytes.ForEach{[char]$_} -join '' Hexadecimal: ("Good to know." | Format-Hex).HexBytes.Split(' ').ForEach{[char][int]::Parse($_,'HexNumber')} -join '' Try: ("Good to know." | Format-Hex). <ctrl>+<space> to know more... — B-Art
– B-Art, Commented Jul 19, 2024 at 7:33
For thos that want to investigate a hexstring: 'E476F6F6420746F206B6E6F772'.ToCharArray().ForEach{if($null -eq $HxSplt){$HxSplt = $_}else{"$HxSplt$_"; $HxSplt=$null}} — B-Art
– B-Art, Commented Jul 19, 2024 at 8:17

Austin T French · Accepted Answer · 2016-07-09 13:21:07Z

8

This is a 3 step process, and although PetSerAl answered it in the comments as a one liner, I'll break it down slightly for posterity (and use a different class).

The first step is to get the Hex number as a decimal (mathematical base 10, not type).

The Second step is the incrementation of the decimal.

And the final step is converting it back to hexadecimal.

broken down and not a one liner this will accomplish the task at hand:

$asDecimal = [System.Convert]::ToInt64("00155DE10B73", 16)
$asDecimal++
$asHex = [System.Convert]::ToString($asDecimal, 16)

answered Jul 9, 2016 at 13:21

Austin T French

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3 Comments

Mathias R. Jessen Over a year ago

Good answer. However Convert.ToInt64() calls Int64.Parse() internally, similarly Convert.ToString(val) calls val.ToString() internally, so technically you are using the same classes as in @PetSerAl's comment :-)

Austin T French Over a year ago

Thanks, @MathiasR.Jessen ! I never looked at the internals and that's good to know.

B-Art Over a year ago

As @MathiasR.Jessen shows, the .parse() method is very powerfull. If you want learn more searching for .parse() or ::parse() will widen your perspective.

Ansgar Wiechers · Accepted Answer · 2016-07-10 15:50:41Z

Another option is to prefix the value with 0x and cast it to an int64:

$Next_MAC_Address = ([int64]"0x$Last_MAC_Address"+1).ToString('X12')

You could also use the format operator (-f) instead of the ToString() method:

$Next_MAC_Address = '{0:X12}' -f ([int64]"0x$Last_MAC_Address"+1)

There is, however, one thing that may be worth noting. MAC addresses aren't just random 6-byte numbers without any inner structure. They actually consist of two parts. The first 3 bytes form the Organizationally Unique Identifier (OUI), a vendor-specific prefix (00-15-5D is one of the OUIs belonging to Microsoft). Only the last 3 bytes are a random number, a unique identifier for each card from the vendor identified by the OUI.

Taking that into consideration you may want to split the MAC address accordingly, e.g. like this:

$oui, $nid = $Last_MAC_Address -split '(?<=^[0-9a-f]{6})(?=[0-9a-f]{6}$)'

or like this:

$oui = $Last_MAC_Address.Substring(0, 6)
$nid = $Last_MAC_Address.Substring(6, 6)

and increment only the NIC identifier, and only if it wouldn't overflow:

if ($nid -ne 'ffffff') {
  $Next_MAC_Address = "{0}{1:X6}" -f $oui, ([int64]"0x$nid"+1)
} else {
  Write-Error 'MAC address overflow.'
}

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