Extract timestamp from filename and sort - sorting

Question

I'm trying to look through each item in a folder and add each item to an array sorted by the datestamp in the filename.
For example, I have three files:
myfile_20150813_040949.txt
myfile_20150812_030949.txt
myfile_20150812_010949.txt
I'm not sure how to parse out the time from each and add them to an array in ascending order. Any help would be appreciated.

Answer 1

I am assuming that you are looking to sort the files by the parsed timestamp that is pulled from the file name with this example. It may not the be the best RegEx approach, but it works in testing.
#RegEx pattern to parse the timestamps
$Pattern = '.*_(\d{4})(\d{2})(\d{2})_(\d{2})(\d{2})(\d{2})\.txt'
$List = New-Object System.Collections.ArrayList
$Temp = New-Object System.Collections.ArrayList
Get-ChildItem | ForEach {
#Make sure the file matches the pattern
If ($_.Name -match $Pattern) {
Write-Verbose "Add $($_.Name)" -Verbose
$Date = $Matches[2],$Matches[3],$Matches[1] -join '/'
$Time = $Matches[4..6] -join ':'
[void]$Temp.Add(
(New-Object PSObject -Property #{
Date =[datetime]"$($Date) $($Time)"
File = $_
}
))
}
}
#Sort the files by the parsed timestamp and add to the main list
$List.AddRange(#($Temp | Sort Date | Select -Expand File))
#Clear out the temp collection
$Temp.Clear()
#Display the results
$List

Answer 2

What you could be doing for this is using the string method .Split() with the [datetime] method of TryParseExact(). Go though each file and add a property for the "FromFileDate" and then sort on that.
$path = "C:\temp"
Get-ChildItem -Filter "*.txt" -Path $path | ForEach-Object{
$date = ($_.BaseName).Split("_",2)[1]
$result = New-Object DateTime
if([datetime]::TryParseExact($date,"yyyyMMdd_hhmmss",[System.Globalization.CultureInfo]::InvariantCulture,[System.Globalization.DateTimeStyles]::None,[ref]$result)){
# This is a good date
Add-Member -InputObject $_ -MemberType NoteProperty -Name "FromFileDate" -Value $result -PassThru
} Else {
# Could not parse date from filename
Add-Member -InputObject $_ -MemberType NoteProperty -Name "FromFileDate" -Value "Could not Parse" -PassThru
}
} | Select-Object Name,fromfiledate | Sort-Object fromfiledate
We take the basename of the each text file and split it into 2 parts from the first underscore. Using TryParseExact we then attempt to convert the "date" string to the format of "yyyyMMdd_hhmmss". Since we use TryParseExact if we have trouble parsing the date then the code will continue.
Sample Output
Name FromFileDate
---- ------------
myfile_20150812_030949.txt 8/12/2015 3:09:49 AM
myfile_20150813_040949.txt 8/13/2015 4:09:49 AM
files.txt Could not Parse
If you didn't want the erroneous data in the output a simple Where-Object{$_.fromfiledate -is [datetime]} would remove those entries.