Powershell - Regex date range replace

Question

I have an input file which contains some start dates and if those dates are before a specific date 1995-01-01 (YYYY-MM-DD format) then replace the date with the minimum value e.g.

<StartDate>1970-12-23</StartDate>

would be changed to

<StartDate>1995-01-01</StartDate>

<StartDate>1996-05-12</StartDate> is ok and would remain unchanged.

I was hoping to use regex replace but checking for the date range isn't working as expected. I was hoping to use something like this for the range check

\b(?:1900-01-(?:3[01]|2[1-31])|1995/01/01)\b

Wiktor Stribiżew · Accepted Answer · 2016-07-11 10:37:02Z

2

You can use a simple regex like '<StartDate>(\d{4}-\d{2}-\d{2})</StartDate>' to match <StartDate>, 4 digits, -, 2 digits, -, 2 digits, and </StartDate>, and then use a callback method to parse the captured into group 1 date and use Martin's code there to compare dates. If the date is before the one defined, use the min date, else, use the one captured.

$callback = {
  param($match)
  $current = [DateTime]$match.Groups[1].Value
  $minimum = [DateTime]'1995-01-01'

  if ($minimum -gt $current)
  {
    '<StartDate>1995-01-01</StartDate>'
  }
  else {
    '<StartDate>' + $match.Groups[1].Value + '</StartDate>'
  }
}

$text = '<StartDate>1970-12-23</StartDate>'
$rex = [regex]'<StartDate>(\d{4}-\d{2}-\d{2})</StartDate>'
$rex.Replace($text, $callback)

To use it with Get-Content and Foreach-Object, you may define the $callback as above and use

$rex = [regex]'<StartDate>(\d{4}-\d{2}-\d{2})</StartDate>'
(Get-Content $path\$xml_in) | ForEach-Object {$rex.Replace($_, $callback)} | Set-Content $path\$outfile

edited Jul 11, 2016 at 10:37

answered Jul 10, 2016 at 10:21

Wiktor Stribiżew

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4 Comments

Wiktor Stribiżew Over a year ago

You still need to use the Regex object as -replace does not support a callback as the replacement. Try (Get-Content $infile) | ForEach-Object {$rex.Replace($_, $callback)} | Set-Content $outfile

zoomzoomvince Over a year ago

I'm pulling this in a from a file with multiple lines so can I do it using a get-Content and Foreach-object (assuming that $_ is the variable for the current line) (Get-Content $path\$xml_out) | Foreach-Object {$rex = [regex]'<StartDate>(\d{4}-\d{2}-\d{\}<\StartDate>', $rex.Replace($_, $callback)} | set-content $path\$xml_out

Wiktor Stribiżew Over a year ago

You should not assign any $rex inside Foreach-Object. Assign $rex before it and only once, and use it as I showed above (I tested it in my Powershell in Win7, and it worked).

zoomzoomvince Over a year ago

Thanks to all that helped especially Wiktor. $xml_in="sample2.xml" $outfile="output.xml" $callback = { param($match) $current = [DateTime]$match.Groups[1].Value $minimum = [DateTime]'1995-01-01' if ($minimum -gt $current) { '<StartDate>1995-01-01</StartDate>' } else { '<StartDate>' + $match.Groups[1].Value + '</StartDate>' } } $rex = [regex]'<StartDate>(\d{4}-\d{2}-\d{2})</StartDate>' #$rex = [regex]'<StartDate>(\d{4}-\d{2}-\d{\})' (Get-Content $path\$xml_in) | ForEach-Object {$rex.Replace($_, $callback)} | Set-Content $path\$outfile

Martin Brandl · Accepted Answer · 2016-07-10 07:10:12Z

1

You don't have to use regex here. Just cast the dates to DateTime and compare them:

$currentDate = [DateTime]'1970-12-23'
$minDate = [DateTime]'1995-01-01'

if ($minDate -gt $currentDate)
{
    $currentDate = $minDate
}

answered Jul 10, 2016 at 7:10

Martin Brandl

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1 Comment

Tomalak Over a year ago

It's not only about the date. The OP should not use regex for the XML parsing, either. Powershell has built-in XML capabilities, it isn't even especially hard to do this properly.

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