Powershell match Regex and Replace - regex

Question

I have a large file that I am searching through to locate and replace invalid dates. I’m using a REGEX expression to locate the dates and then determining if they are valid or not. If the script finds an invalid date it needs to replace the date with the current date. For audit purposes I need to record the invalid string and the line number on which the error was found. So far (with some prior help to SO) I have been able to locate the invalid dates, but I have not been able to successfully change them.
This is the code I’m using to locate the invalid dates. How can I locate and change the date in a single pass?
$matchInfos = #(Select-String -Pattern $regex -AllMatches -Path $file)
foreach ($minfo in $matchInfos)
{
#"LineNumber $($minfo.LineNumber)"
foreach ($match in #($minfo.Matches | Foreach {$_.Groups[0].value}))
{
if (([Boolean]($match -as [DateTime]) -eq $false ) -or ([DateTime]::parseexact($match,"MM-dd-yyyy",$null).Year -lt "1800")) {
Write-host "Invalid date on line $($minfo.LineNumber) - $match"
#Add-Content -Path $LOGFILE -Value "Invalid date on line $($minfo.LineNumber) - $match"
# Replace the invalid date with a corrected one
Write-Host "Replacing $match with $(Get-Date -Format "MM-dd-yyyy")"
#Add-Content -Path $LOGFILE -Value "Replacing $match with $(Get-Date -Format "MM-dd-yyyy")"
}
}
}

Answer 1

You have to write out a temporary file with the changes and replace the file with the temporary. Here's one I wrote that will do that part for you:
Windows IT Pro: Replacing Strings in Files Using PowerShell
Example of use:
replace-filestring -pattern 'find' -replacement 'replace' -path myfile.txt -overwrite
With this command, the script will read myfile.txt, replace 'find' with 'replace', write the output to a temporary file, and then replace myfile.txt with the temporary file. (Without the -Overwrite parameter, the script will only output the contents of myfile.txt with the changes.)
Bill

Answer 2

$lines = get-content $file
$len = $lines.count
$bad = #{}
for($i=0;$i-lt$len;$i++){
if($lines[$i] -match ""){
$bad_date = $lines[$i].substring(10) #Get the bad date
$good_date = Get-Date -Format G
$bad["$i"] += #($line[$i])
$lines[$i] = $lines[$i].Replace($bad_date,$good_date)
}
}
$lines > $NewFile
$bad > $bad_date_file
Here is some pseudo code of how I would combat this problem. Not sure how big your file is. Reading and writing could be slow.