Powershell- match split and replace based on index - powershell

Question

I have a file
AB*00*Name1First*Name1Last*test
BC*JCB*P1*Church St*Texas
CD*02*83*XY*Fax*LM*KY
EF*12*Code1*TX*1234*RJ
I need to replace the 5th element in the CD segment alone from LM to ET in each of the file in the folder. Element delimiter is * as mentioned in the above sample file content. I am new to PowerShell and tried a code as below but unfortunately it is not giving desired results. Can any of you please provide some help?
foreach($xfile in $inputfolder)
{
If ($_ match "^CD\*")
{
[System.IO.File]::ReadAllText($xfile).replace(($_.split("*")[5],"ET") | Set-Content $xfile
}
[System.IO.File]::WriteAllText($xfile),((Get-Content $xfile -join("~")))
}

Answer 1

here's a slightly different way to get there ... [grin] what it does ...
fakes reading in a test file
when ready to do this for real, remove the entire #region/#endregion block and use Get-Content.
sets the constants
iterates thru the imported text file lines
checks for a line that starts with the target pattern
if found ...
== escapes the old value with [regex]::Escape() to deal with the asterisks
== replaces the escaped old value with the new value
== outputs the new version of that line
if NOT found, outputs the line as-is
stores all the lines into the $OutStuff var
displays that on screen
the code ...
#region >>> fake reading in a plain text file
# in real life, use Get-Content
$InStuff = #'
AB*00*Name1First*Name1Last*test
BC*JCB*P1*Church St*Texas
CD*02*83*XY*Fax*LM*KY
EF*12*Code1*TX*1234*RJ
'# -split [System.Environment]::NewLine
#endregion >>> fake reading in a plain text file
$TargetLineStart = 'CD*'
$OldValue = '*LM*'
$NewValue = '*ET*'
$OutStuff = foreach ($IS_Item in $InStuff)
{
if ($IS_Item.StartsWith($TargetLineStart))
{
$IS_Item -replace [regex]::Escape($OldValue), $NewValue
}
else
{
$IS_Item
}
}
$OutStuff
output ...
AB*00*Name1First*Name1Last*test
BC*JCB*P1*Church St*Texas
CD*02*83*XY*Fax*ET*KY
EF*12*Code1*TX*1234*RJ
i will leave saving that to a new file [or overwriting the old one] to the user. [grin]

Answer 2

You could capture all that comes before the match in group 1, and match LM.
In the replacement use $1ET
^(CD*(?:[^*\r\n]+\*){5})LM\b
Regex demo
If you don't want to match LM literally, you could also match any other char than * or a newline.
^(CD*(?:[^*\r\n]+\*){5})[^*\r\n]+\b
Replace example
$allText = Get-Content -Raw file.txt
$allText -replace '(?m)^(CD*(?:[^*\r\n]+\*){5})LM\b','$1ET'
Output
AB*00*Name1First*Name1Last*test
BC*JCB*P1*Church St*Texas
CD*02*83*XY*Fax*ET*KY
EF*12*Code1*TX*1234*RJ