Masking fields duplications - powershell

Question

I am trying to mask fields in a string as seen below. It is working to an extent, half way really. At some stage after the $addresspostcode the replacement characters aren't replacing for the correct positions. Would anyone have an idea of a fix?
The adressee0 line is from the output file
ADDRESSEE0|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY|YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY|YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY|YYYYYYYYYYYYYYYYYYYYYYYYYYYYYY|ZZZZZZZZ|Sir or MadamZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |A1|OM|Mr Patrick MurphyZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|45 CregtownZZZZZZZZZZZZZZZZ |EastRoad RoadZZZZZZZZZZZZZZZZ |TownnamersZZZZZZZZZZZZZZZZ |CityAB 16ZZZZZZZZZZZZZZZZ |ZZZZZZZZ| |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX|ZZZZZZZZZZZZZZZZ |Sir or MadamZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |IA|3319041| | |XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXZZZZZZZZ
ForEach-Object {
$addresseeName = $_.Substring(11,50)
$addresseeName2 = $_.Substring(62,50)
$addresseeLine1 = $_.Substring(113,30)
$addresseeLine2 = $_.Substring(144,30)
$addresseeLine3 = $_.Substring(175,30)
$addresseeLine4 = $_.Substring(206,30)
$addresseePostCode = $_.Substring(237,8)
$referenceAddressName1 = $_.Substring(303,50)
$referenceAddressName2 = $_.Substring(354,50)
$referenceAddresseeLine1 = $_.Substring(405,30)
$referenceAddresseeLine2 = $_.Substring(436,30)
$referenceAddresseeLine3 = $_.Substring(467,30)
$referenceAddresseeLine4 = $_.Substring(498,30)
$mask50 = 'X' * 50
$mask30 = 'Y' * 30
$mask08 = 'Z' * 8
# IF statement, if the string is at position 0-10, and begins with 'ADDRESSEE0'
# then run replace statement
if ($_.Substring(0,10) -eq 'ADDRESSEE0') {
$_.Replace($addresseeName, $mask50).Replace($addresseeName2, $mask50).Replace($addresseeLine1, $mask30).Replace($addresseeLine2, $mask30).Replace($addresseeLine3, $mask30).Replace($addresseeLine4, $mask30).Replace($addresseePostCode, $mask08).Replace($referenceAddressName1, $mask50).Replace($referenceAddressName2, $mask50).Replace($referenceAddresseeLine1, $mask30).Replace($referenceAddresseeLine2, $mask30).Replace($referenceAddresseeLine3, $mask30).Replace($referenceAddresseeLine4, $mask30)

Answer 1

The problem with your code is that it does the replace based on the contents of the string (rather than the position). This means if the same text exists elsewhere in the string, it replaces that text also, breaking the later replaces.
I suggest you do this instead:
$mask50 = 'X' * 50
$mask30 = 'Y' * 30
$mask08 = 'Z' * 8
$SomeInput | ForEach-Object {
if ($_.Substring(0,10) -eq 'ADDRESSEE0')
{
$SplitString = $_.Split('|')
1..2 | ForEach-Object { $SplitString[$_] = $mask50 }
3..6 | ForEach-Object { $SplitString[$_] = $mask30 }
$SplitString[7] = $mask08
8..9 | ForEach-Object { $SplitString[$_] = $mask50 }
10..13 | ForEach-Object { $SplitString[$_] = $mask30 }
$SplitString -Join '|'
}
}
This splits the string based on the | character and then does individual replaces for each (we use the .. array notation to make this a little more efficient).
Then we join the string again at the end with the | character.

Answer 2

Assuming ADDRESSEE0|... is the input string, why not split the data first? This provides manageable chunks instead of one giant string with truckload of method chaining. Like so,
# Get input data
$raw = `'ADDRESSEE0|ADDRESSEE1|ADDRESSEELine0|ADDRESSEELine1|...'`
# Split the string by each pipe | char. This uses regex syntax, so escape \ is needed
$lines = $raw -split '\|'
# Assign splitted elements into more readable variables
$addresseeName = $lines[0]
$addresseeName2 = $lines[1]
$addresseeLine1 = $lines[2]
...
# mask the data whatever way floats your boat
$addresseeName = $addresseeName.substring(0,9) + $mask08