Powershell script to replace pattern YY to YYYY-CodePudding

I am not the Powershell pro so I need some help.

What I have now is for example:

somelongname_08-01-01_someotherlongname.pdf

and I want a rename to

somelongname_2008-01-01_someotherlongname.pdf

In short changing two digit year format to four digit year format within the name of multiple files.

At the moment I use the following script to rename all files in a specific folder:

get-childitem *.* | foreach { rename-item $_ $_.Name.Replace("_08-", "_2008-") }

I do not want to achieve it by copying the above formula to:
...
get-childitem *.* | foreach { rename-item $_ $_.Name.Replace("_08-", "_2008-") }
get-childitem *.* | foreach { rename-item $_ $_.Name.Replace("_09-", "_2009-") }
get-childitem *.* | foreach { rename-item $_ $_.Name.Replace("_10-", "_2010-") }
...

So is there a more elegant and fast way, because the years may vary from - 1925-2023

The basic search and replace pattern is always the same and its's unique in each filename and begins with _ contains two numbers for the year and ends with -.

So I have two cases
-) years from 25 to 99 need at the beginning an "19"
-) years from 00 to 23 need at the beginning an "20"

Thanks in advance

CodePudding user response：

You can use Regex.Replace(String, String, MatchEvaluator) to handle the logic if 20 or 19 should be prepended to the string, for example:

$re = [regex] '(?<=_)\d{2}'

'somelongname_08-01-01_someotherlongname.pdf',
'somelongname_25-01-01_someotherlongname.pdf',
'somelongname_24-01-01_someotherlongname.pdf' | ForEach-Object {
    $re.Replace($_, {
        switch($args[0].Value) {
            { $_ -ge 25 -and $_ -le 99 } {
                return '19'   $_
            }
            { $_ -ge 0 -and $_ -le 23 } {
                return '20'   $_
            }
            # leave it as-is if it didn't match the above conditions
            Default { $_ }
        }
    })
}

If this is what you were looking for, you can include it to your Rename-Item:

$re = [regex] '(?<=_)\d{2}'

Get-ChildItem -Filter *.pdf | Rename-Item -NewName {
    $re.Replace($_.Name, {
        switch($args[0].Value) {
            { $_ -ge 25 -and $_ -le 99 } {
                return '19'   $_
            }
            { $_ -ge 0 -and $_ -le 23 } {
                return '20'   $_
            }
            Default { $_ }
        }
    })
}

CodePudding user response：

Normally, the century that is chosen will depend on the half-century year, so if the two-digit year is 50, this will be regarded as 1950 and anything below 50 will become 20xx

You can use .Net for this:

(Get-ChildItem -Path 'D:\Test' -Filter '*_*_*.pdf' -File) | ForEach-Object { 
    # split the file BaseName in three parts
    $prefix, $date, $postfix = $_.BaseName -split '_', 3
    # let .Net parse out the date. 
    # Up to and including year 49, this century is used, year 50 and above will become the 1900's
    $date = [datetime]::ParseExact($date,'yy-MM-dd', $null)
    $newName = '{0}_{1:yyyy-MM-dd}_{2}{3}' -f $prefix, $date, $postfix, $_.Extension
    $_ | Rename-Item -NewName $newName
}

Result:

somelongname_08-01-01_someotherlongname.pdf --> somelongname_2008-01-01_someotherlongname.pdf
somelongname_25-01-01_someotherlongname.pdf --> somelongname_2025-01-01_someotherlongname.pdf
somelongname_49-01-01_someotherlongname.pdf --> somelongname_2049-01-01_someotherlongname.pdf
somelongname_50-01-01_someotherlongname.pdf --> somelongname_1950-01-01_someotherlongname.pdf

If however you have good reason to deviate from this, you can do:

(Get-ChildItem -Path 'D:\Test' -Filter '*_*_*.pdf' -File) | ForEach-Object { 
    # split the file BaseName in three parts
    $prefix, $date, $postfix = $_.BaseName -split '_', 3
    $century = if ([int]$date.Substring(0,2) -ge 25) { 19 } else { 20 }
    $newName = '{0}_{1}{2}_{3}{4}' -f $prefix, $century, $date, $postfix, $_.Extension
    $_ | Rename-Item -NewName $newName
}

Result now:

somelongname_08-01-01_someotherlongname.pdf --> somelongname_2008-01-01_someotherlongname.pdf
somelongname_25-01-01_someotherlongname.pdf --> somelongname_1925-01-01_someotherlongname.pdf
somelongname_49-01-01_someotherlongname.pdf --> somelongname_1949-01-01_someotherlongname.pdf
somelongname_50-01-01_someotherlongname.pdf --> somelongname_1950-01-01_someotherlongname.pdf