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I am trying to create a function for a larger script to determine the third octet of a site IP address based off a user entered site number. I have actually come up with the function, but was hoping that someone could help me come up with something that is simpler and more elegant, instead of the multitude of nested if statements that I came up with. Here are the rules:

• For sites numbered 0001 - 0255, the third octet is the last 3 digits of the site number, less any zeroes preceding a real number (e.g. Site 0007 = 10.10.7.xxx)


• For sites numbered 0256 - 0399 and 0500 - 1999 (except 1202), the third octet is the last 2 digits of the site number less any zeroes preceding a real number (e.g. site 0315 = 10.22.15.xxx)


• For sites numbered 401 - 499, the third octet is the last two digits of the site number +100 (e.g. 0401 = 10.20.101.xxx)


• Site 1202 is an exception to the above rule, where the third octet is the last 3 digits (.202)


• For sites 5000 and above (5000 - 9999), the first digit is dropped, and then the rules above are followed. (e.g. 8248 = 10.12.48.xxx)

Here is what I have come up with. It is not very elegant, but it seems to work. Note that the first three lines will be in another function in the script, but are here for testing purposes.

$global:site = Read-Host 'What is the 4 digit site number?' #must include leading zeros
[int]$global:sitecheck=$site #need for comparasion operators
[string]$global:sitestring=$site

if ($sitecheck -le 255)
 
 if ($sitestring.substring(0,3) -eq '000') #(i.e. 0001 - 0009)
 
 $global:thirdoct = $sitestring.substring(3,1) #(i.e. 1-9)
 
 elseif ($sitestring.substring(0,2) -eq '00') #(i.e. 0010 - 0099) 
 
 $global:thirdoct = $sitestring.substring(2,2) #(i.e. 10 - 99)
 
 elseif ($sitestring.substring(0,1) -eq '0') #(i.e. 0100 - 0255)
 
 $global:thirdoct = $sitestring.substring(1,3) #(i.e. 100 - 255)
 
 
elseif ($sitecheck -ge 256 -and $sitecheck -le 399 ) 
 
 if ($sitestring.substring(2,1) -eq '0') 
 
 $global:thirdoct = $sitestring.substring(3,1)
 
 else
 
 $global:thirdoct = $sitestring.substring(2,2)
 

elseif ($sitecheck -ge 401 -and $sitecheck -le 499) 
 
 $global:thirdoct = 100+$sitestring.substring(2,2)
 
elseif ($sitecheck -ge 501 -and $sitecheck -le 799) 
 
 if ($sitestring.substring(2,1) -eq '0')
 
 $global:thirdoct = $sitestring.substring(3,1)
 
 else
 
 $global:thirdoct = $sitestring.substring(2,2)
 
 
elseif ($sitecheck -eq 1202)
 
 $global:thirdoct = $sitestring.substring(1,3)
 
elseif ($sitecheck -ge 5000 -and $sitecheck -le 9999) 
 
 $site5000 = [int]$sitestring.substring(1,3)
 if ($site5000 -le 255)
 
 if ($sitestring.substring(1,2) -eq '00')
 
 $global:thirdoct = $sitestring.substring(3,1)
 
 elseif ($sitestring.substring(1,1) -eq '0')
 
 $global:thirdoct = $sitestring.substring(2,2)
 
 else 
 
 $global:thirdoct = $sitestring.substring(1,3)
 
 
 elseif (($site5000 -ge 256 -and $site5000 -le 399) -or ($site5000 -ge 501 -and $site5000 -le 999))
 
 $global:thirdoct = $sitestring.substring(2,2)
 
 elseif ($site5000 -ge 401 -and $site5000 -le 499)
 
 $global:thirdoct = 100+$sitestring.substring(2,2)