Powershell regular expressions: get 'not matched' portion of string? - regex

Question

I'm not very up on powershell and have a problem.
I have a powershell script that calls a batch file that mounts a backup image (shadowprotect), runs chkdsk against mounted image, dismounts image and returns.
All the output from the batch file processing is returned to my powershell script.
I'm trying to parse this to remove all the 'progress' lines that get generated by the chkdsk command, chkdsk doesn't seem to have any way to suppress this output (on large disk images I can end up with hundreds of progress lines).
I can create regular expression to catch all the 'Progress' lines and put them out to my log file, but I can't figure out the syntax that says to give me everything that does NOT match my regular expression.
Very short example of returned value I'm trying to parse:
Try to mount d:\backups\colt\F_VOL-b001-i453-cd.spi
Mounting image chain "D:\Backups\colt\F_VOL-b001.spf|D:\Backups\colt\F_VOL-b001-i014-cd-cw.spi|D:\Backups\colt\F_VOL-b001-i018-cd.spi|D:\Backups\colt\F_VOL-b001-i022-cd.spi|D:\Backups\colt\F_VOL-b001-i026-cd.spi|D:\Backups\colt\F_VOL-b001-i030-cd.spi|D:\Backups\colt\F_VOL-b001-i445-cd.spi|D:\Backups\colt\F_VOL-b001-i449-cd.spi|D:\Backups\colt\F_VOL-b001-i453-cd.spi"
The type of the file system is NTFS.
Volume label is Local Disk - single.
WARNING! F parameter not specified.
Running CHKDSK in read-only mode.
Stage 1: Examining basic file system structure ...
Progress: 0 of 4320 done; Stage: 0%; Total: 0%; ETA: 0:00:14
Progress: 0 of 4320 done; Stage: 0%; Total: 0%; ETA: 0:00:21 .
Progress: 6 of 4320 done; Stage: 0%; Total: 0%; ETA: 0:01:10 ..
Progress: 257 of 4320 done; Stage: 5%; Total: 2%; ETA: 0:01:47 ...
Progress: 769 of 4320 done; Stage: 17%; Total: 6%; ETA: 0:01:20
Progress: 2817 of 4320 done; Stage: 65%; Total: 19%; ETA: 0:00:23 .
Progress: 4320 of 4320 done; Stage: 100%; Total: 29%; ETA: 0:00:14 ..
4320 file records processed.
File verification completed.
Progress: 0 of 0 done; Stage: 99%; Total: 46%; ETA: 0:00:13 ...
0 large file records processed.
Progress: 0 of 0 done; Stage: 99%; Total: 46%; ETA: 0:00:13
0 bad file records processed.
Stage 2: Examining file name linkage ...
Progress: 4322 of 4360 done; Stage: 99%; Total: 92%; ETA: 0:00:01 .
Progress: 4340 of 4360 done; Stage: 99%; Total: 93%; ETA: 0:00:01 ..
Progress: 4344 of 4360 done; Stage: 99%; Total: 97%; ETA: 0:00:01 ...
Progress: 4360 of 4360 done; Stage: 100%; Total: 97%; ETA: 0:00:01
4360 index entries processed.
Index verification completed.
Progress: 0 of 0 done; Stage: 99%; Total: 97%; ETA: 0:00:01 .
0 unindexed files scanned.
Progress: 0 of 0 done; Stage: 99%; Total: 97%; ETA: 0:00:01 ..
0 unindexed files recovered.
Stage 3: Examining security descriptors ...
Security descriptor verification completed.
Progress: 0 of 0 done; Stage: 100%; Total: 99%; ETA: 0:00:00 ...
20 data files processed.
Windows has scanned the file system and found no problems.
No further action is required.
145500673 KB total disk space.
15814844 KB in 748 files.
180 KB in 22 indexes.
0 KB in bad sectors.
74721 KB in use by the system.
65536 KB occupied by the log file.
129610928 KB available on disk.
4096 bytes in each allocation unit.
36375168 total allocation units on disk.
32402732 allocation units available on disk.
OK - 0
Return value is 0
My script fragment looks like this:
# call batch file...
$Out = c:\batch\Mount_and_Chkdsk_image_file.cmd $NewFilePath
# append result of batch file to the log file, remove progress lines first...
$Out -replace ("^Progress:.*$", "")
Out-File -FilePath c:\batch\log\NewFileCheck.log -Append -InputObject $Out
In above attempt, since I can match the progress lines I thought I'd just replace them with nothing but no substitution happened.
(for testing I substituted the batch file call with just a file read of the raw unfiltered log file:
$FilePath = "c:\batch\test2.txt"
$Out = [System.Io.File]::ReadAllText($filePath)
)
Anyway, since replacement didn't work, I used google and tried understanding the select-string as an option since it takes regular expressions:
$Regex = 'Pattern:.*'
$Out | select-string -pattern $Regex -notmatch
This just puts out all the lines, nothing filtered out, I had hoped 'notmatch' would mean everything that didn't match. Didn't seem to matter how I varied regex I couldn't get that to do what I needed.
Tried many many more variations on the theme like:
#$Regex = '^((Progress:).*$)'
$Regex = '([?<!Progress:].*)'
$Out | Select-String -Pattern $Regex -AllMatches | %{$_.Matches } | %{$_.value}
But I'm obviously missing something. I would have thought there would be an easy function that if you could select a certain string you could also choose to not have that selection in the output.
Can anyone please help, how do I capture all the lines that aren't a match?
Regards,
Bryce S.

Answer 1

Sure, this can be done. By default when you load a text file with Get-Content it will load each line as a string, and the entire file will be an array of strings. You can run that through a Where statement and use the -notmatch operator to filter out things. Usage would be as such:
$ParsedData = Get-Content "c:\batch\test2.txt" | Where{$_ -notmatch "Progress:.*$"}
That would assist $ParsedData all of the lines in the file that did not match the regex "Progress:.*$".
Edit: Ok, what you're getting from your script is most likely a multi-line string. The easiest way that I know of is to simply break your string up on the new lines to make an array of strings. Something like this:
$Out.Split("`n") | Where{$_ -notmatch "Progress:.*$"}

Answer 2

$Out = $Out -replace ("^Progress:.*$", "")
Out-File -FilePath c:\batch\log\NewFileCheck.log -Append -InputObject $Out
The only problem you had was that -replace doesn't modify the left side value, it just returns the result, leaving $Out unchanged, so you have to make sure you assign the result back to $Out.