Add capture group values in a PowerShell replace loop - regex

Question

Needing to replace a string in multiple text files with the same string , except with capture group 2 replaced by the sum of itself and capture group 4.
String: Total amount $11.39 | Change $0.21
Desired Result: Total amount $11.60 | Change $0.21
I have attempted several methods. Here is my last attempt which seems to run without error, but without any changes to the string .
$Originalfolder = "$ENV:userprofile\Documents\folder\"
$Originalfiles = Get-ChildItem -Path "$Originalfolder\*"
$RegexPattern = '\b(Total\s\amount\s\$)(\d?\d?\d?\d?\d\.?\d?\d?)(\s\|\sChange\s\$)(\d?\d?\d\.?\d?\d?)\b'
$Substitution = {
Param($Match)
$Result = $GP1 + $Sumtotal + $GP3 + $Change
$GP1 = $Match.Groups[1].Value
$Total = $Match.Groups[2].Value
$GP3 = $Match.Groups[3].Value
$Change = $Match.Groups[4].Value
$Sumtotal = ($Total + $Change)
return [string]$Result
}
foreach ($file in $Originalfiles) {
$Lines = Get-Content $file.FullName
$Lines | ForEach-Object {
[Regex]::Replace($_, $RegexPattern, $Substitution)
} | Set-Content $file.FullName
}

Answer 1

For one thing, your regular expression doesn't even match what you're trying to replace, because you escaped the a in amount:
\b(Total\s\amount\s\$)(\d?\d?\d?...
# ^^
\a is an escape sequence that matches the "alarm" or "bell" character \u0007.
Also, if you want to calculate the sum of two captures you need to convert them to numeric values first, otherwise the + operator would just concatenate the two strings.
$Total = $Match.Groups[2].Value
$Change = $Match.Groups[4].Value
$Sumtotal = $Total + $Change # gives 11.390.21
$Sumtotal = [double]$Total + [double]$Change # gives 11.6
And you need to build $Result after you defined the other variables, otherwise the replacement function would just return an empty string.
Change this:
$RegexPattern = '\b(Total\s\amount\s\$)(\d?\d?\d?\d?\d\.?\d?\d?)(\s\|\sChange\s\$)(\d?\d?\d\.?\d?\d?)\b'
$Substitution = {
param ($Match)
$Result = $GP1 + $Sumtotal + $GP3 + $Change
$GP1 = $Match.Groups[1].Value
$Total = $Match.Groups[2].Value
$GP3 = $Match.Groups[3].Value
$Change = $Match.Groups[4].Value
$Sumtotal = ($Total + $Change)
return [string]$Result
}
into this:
$RegexPattern = '\b(Total\samount\s\$)(\d?\d?\d?\d?\d\.?\d?\d?)(\s\|\sChange\s\$)(\d?\d?\d\.?\d?\d?)\b'
$Substitution = {
Param($Match)
$GP1 = $Match.Groups[1].Value
$Total = [double]$Match.Groups[2].Value
$GP3 = $Match.Groups[3].Value
$Change = [double]$Match.Groups[4].Value
$Sumtotal = ($Total + $Change)
$Result = $GP1 + $Sumtotal + $GP3 + $Change
return [string]$Result
}
and the code will mostly do what you want. "Mostly", because it will not format the calculated number to double decimals. You need to do that yourself. Use the format operator (-f) and change your replacement function to something like this:
$Substitution = {
Param($Match)
$GP1 = $Match.Groups[1].Value
$Total = [double]$Match.Groups[2].Value
$GP3 = $Match.Groups[3].Value
$Change = [double]$Match.Groups[4].Value
$Sumtotal = $Total + $Change
return ('{0}{1:n2}{2}{3:n2}' -f $GP1, $Sumtotal, $GP3, $Change)
}
As a side note: the sub-expression \d?\d?\d?\d?\d\.?\d?\d? could be shortened to \d+(?:\.\d+)? (one or more digit, optionally followed by a period and one or more digits) or, more exactly, to \d{1,4}(?:\.\d{0,2})? (one to four digits, optionally followed by a period and up to 2 digits).

Answer 2

here's how I'd do it: this is pulled out of a larger script that regularly scans a directory for files, then does a similar manipulation, and I've changed variables quickly to obfuscate, so shout if it doesn't work and I'll take a more detailed look tomorrow.
It takes a backup of each file as well, and works on a temp copy before renaming.
Note it also sends an email alert (code at the end) to say if any processing was done - this is because it's designed to run as as scheduled task in the original
$backupDir = "$pwd\backup"
$stringToReplace = "."
$newString = "."
$files = #(Get-ChildItem $directoryOfFiles)
$intFiles = $files.count
$tmpExt = ".tmpDataCorrection"
$DataCorrectionAppend = ".DataprocessBackup"
foreach ($file in $files) {
$content = Get-Content -Path ( $directoryOfFiles + $file )
# Check whether there are any instances of the string
If (!($content -match $stringToReplace)) {
# Do nothing if we didn't match
}
Else {
#Create another blank temporary file which the corrected file contents will be written to
$tmpFileName_DataCorrection = $file.Name + $tmpExt_DataCorrection
$tmpFile_DataCorrection = $directoryOfFiles + $tmpFileName_DataCorrection
New-Item -ItemType File -Path $tmpFile_DataCorrection
foreach ( $line in $content ) {
If ( $line.Contains("#")) {
Add-Content -Path $tmpFile_DataCorrection -Value $line.Replace($stringToReplace,$newString)
#Counter to know whether any processing was done or not
$processed++
}
Else {
Add-Content -Path $tmpFile_DataCorrection -Value $line
}
}
#Backup (rename) the original file, and rename the temp file to be the same name as the original
Rename-Item -Path $file.FullName -NewName ($file.FullName + $DataCorrectionAppend) -Force -Confirm:$false
Move-Item -Path ( $file.FullName + $DataCorrectionAppend ) -Destination backupDir -Force -Confirm:$false
Rename-Item -Path $tmpFile_DataCorrection -NewName $file.FullName -Force -Confirm:$false
# Check to see if anything was done, then populate a variable to use in final email alert if there was
If (!$processed) {
#no message as did nothing
}
Else {
New-Variable -Name ( "processed" + $file.Name) -Value $strProcessed
}
} # Out of If loop
}