Using Context in Powershell Select-String

Question

I have a script that searches for a series of strings (stored in a txt file) in the contents of files in a directory. I would like to modify it to also list the text around the string found (these are regular strings, not regex expressions). I played around a lot and it seems like I need to use -Context, but I am not sure how to get the text from that.

Also, the files I am searching may not have linefeeds, so if it could just get the xx characters before and after the search term, that would be better.

Here's what I have so far (I omitted the looping though files parts):

$result = Get-Content $file.FullName | Select-String $control -quiet  
If ($result -eq $True) 
{ 
  $match = $file.FullName 
  "Match on string :  $control  in file :  $match" | Out-File $output -Append 
  Write-host "Match on string :  $control  in file :  $match"
}

If it could write the context, that would be perfect. Seems like I need to use $_Matches, but not sure how.

Ansgar Wiechers · Accepted Answer · 2013-01-03 23:58:55Z

1

If $control is just a regular string, can you turn it into a regular expression?

$n  = 3
$re = "(.{0,$n})(" + [Regex]::Escape($control) + ")(.{0,$n})"

$result = (Get-Content $file.FullName) -match $re

With this, the $matches hashtable should give you access to the $n characters before and after the match:

if ($result.Length -gt 0) {
  echo "Before: $($matches[1])"
  echo "After:  $($matches[3])"
}

edited Jan 3, 2013 at 23:58

answered Jan 3, 2013 at 23:48

Ansgar Wiechers

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5 Comments

Joey Over a year ago

You can also modify the check to if ($result) which (in my eyes) reads nicer. But maybe I golf too much in PowerShell ;)

Ansgar Wiechers Over a year ago

That would make $result look like a boolean value, which it isn't. I prefer to avoid this kind of confusion, even if the language allows it.

Joey Over a year ago

Ah, fair enough. In PowerShell < 3 you might get an error then when the file only contains a single matching line :-). (Granted, when using just $result you'd get problems with a single matching line too, if it's an empty string, but that's unlikely given the scenario.)

user1612851 Over a year ago

I get a lot of "the variable '$matches' cannot be retrieved because it has not been set."

user1612851 Over a year ago

I also think if the characters right before or after were a line feed, it wouldn't find a match. I think using [\s\S] might get around that.

Community · Accepted Answer · 2013-04-18 12:18:40Z

0

Here is what I have now and it seems to work:

  $regex = "[\s\S]{0,$ContextChars}$SearchTerm[\s\S]{0,$ContextChars}"
  $results = Get-Content $file.FullName | Select-String -Pattern $regex -AllMatches | % { $_.Matches } | % { $_.Value }      

  if ($results)
  {
    foreach($result in $results)
    {
      $display = $result
      "File: $file   Match ---$display---"  
    }
  }

The only thing I wish I had but don't know how to get it is the line number the match is found on.

edited Apr 18, 2013 at 12:18

CommunityBot

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answered Jan 4, 2013 at 22:09

user1612851

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