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PowerShell script to find a string and delete all lines in a text file that do not have it

Posted on 2011-09-23
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Last Modified: 2012-05-12
I am wondering if it's possible to create a powershell script to do the following:

Find a value of lets say 123 in a text file

The value of 123 is in Line 2 of the text file but not Line 1 or 3.

I want it to delete line 1 and 3 but save line 2.

This would need to be done for thousands of lines.

Is this possible? Powershell or DOS, VB?

thanks in advance
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Question by:awgit
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chrismerritt earned 500 total points
ID: 36589847
Try this, but please test it first. i.e backup the file you are testing against.

Will overwrite the specified file content with any lines that contain the word in the $match variable. i.e. it will only keep lines that match your requirements, all other lines will be removed.

#Customise Vars
$SourceFile = "C:\TEMP\test.txt"
$Match = "123"

(Get-Content $SourceFile) | % {if ($_ -match $Match){$_}} | Set-Content $SourceFile

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Author Comment

by:awgit
ID: 36589978
That worked!

As I was testing myself I just found another command that also worked. Instead of modifying the original file it exports out the results to another file

This is the command that does that:
get-childitem C:\scripts\source.txt | select-string -pattern 123 | foreach {$_.line} > C:\scripts\123.txt
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Expert Comment

by:chrismerritt
ID: 36590292
No problem, you could save to another file by modifying my code as follows as well:

#Customise Vars
$SourceFile = "C:\TEMP\test.txt"
$DestinationFile = "C:\TEMP\new.txt"
$Match = "123"

(Get-Content $SourceFile) | % {if ($_ -match $Match){$_}} | Set-Content $DestinationFile

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