Question

Delete line from text file

Asked by: traigo

I am trying to write a VBS that will remove a line from a text file if it contains a certain string value.  I've got most of the way through, except for the part about deleting the line.  That's where I'm stuck.  The VBS will read all text files in the current directory, and remove lines from the text files based on a string comparison.

I've looked up some solutions to deleting a line from a text file, or replacing strings.  They all: opend the file, read the lines with a comparison, concantenated a string, closed the file, opened the file for writing and wrote the concantenated string.  I understand that this is very slow and I don't want to do this.  Currently, just the below code takes about 30 seconds to run.  I have lots of text files and the smaller ones have around 50,000 lines (though mostly made up of the line I'm trying to remove).

How do I delete a line?  That's the only part I'm missing.

Option Explicit

dim filepath, VBSName, objFSO, objTextFile
dim fs, folder, file, item, line
VBSname = wscript.scriptfullname

Filepath = left(VBSname, Len(VBSname) -(len(VBSname) - InstrRev(VBSname, "\")))

     set fs = CreateObject("Scripting.FileSystemObject")
     set folder = fs.GetFolder(FilePath)

     for each item in folder.Files
      If Right(item.name, 3) = "txt" Then

      Set objFSO = CreateObject("Scripting.FileSystemObject")
      Set objTextFile = objFSO.OpenTextFile (item, 1)

      Do Until objTextFile.AtEndOfStream
          Line = objTextFile.ReadLine
            If InStr(1,Line, " Host Domain: ",1)  Then

            Else

            End If
      Loop
      
      set objFSO = nothing
      set objTextFile = nothing
      End If
     next
msgbox "Done!"

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Asked On
2006-01-13 at 17:32:42ID21696282
Tags

line

,

delete

,

file

,

text

,

from

Topic

VB Controls

Participating Experts
2
Points
500
Comments
15

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Answers

 

by: amit_gPosted on 2006-01-13 at 17:53:10ID: 15697997

This is probably as fast as it can get with VBScript ...

Option Explicit

dim filepath, VBSName, objFSO, objTextFile
dim fs, folder, file, item, Body
Dim oRegExp

VBSname = wscript.scriptfullname

Filepath = left(VBSname, Len(VBSname) -(len(VBSname) - InstrRev(VBSname, "\")))

Set objFSO = CreateObject("Scripting.FileSystemObject")

set fs = CreateObject("Scripting.FileSystemObject")
set folder = fs.GetFolder(FilePath)

Set oRegExp = New RegExp
oRegExp.Pattern = " Host Domain: .*\n"
oRegExp.IgnoreCase = True
oRegExp.Global = True
oRegExp.MultiLine = True

for each item in folder.Files
      If Right(item.name, 3) = "txt" Then
            Set objTextFile = objFSO.OpenTextFile (item, 1)
            Body = objTextFile.ReadAll
            set objTextFile = nothing

            Body = oRegExp.Replace(Body, "")

            Set objTextFile = objFSO.CreateTextFile (item, True)
            Call objTextFile.Write(Body)
            set objTextFile = nothing
      End If
next

set objFSO = nothing

msgbox "Done!"

 

by: traigoPosted on 2006-01-13 at 18:04:14ID: 15698038

That deleted the strings and the VBCRLF, but not the entire line.

 

by: amit_gPosted on 2006-01-13 at 18:05:59ID: 15698044

Could you please post few sample lines having the strings.

 

by: traigoPosted on 2006-01-13 at 18:09:18ID: 15698056

1/13/2006 8:05:46 PM - (  1411) HOST domain:
1/13/2006 8:05:46 PM - (  1419) HOST domain:
1/13/2006 8:05:46 PM - (  1418) HOST domain:
1/13/2006 8:05:46 PM - (  1411) HOST domain:
1/13/2006 8:05:46 PM - (  1413) HOST domain:

 

by: amit_gPosted on 2006-01-13 at 18:10:12ID: 15698059

Change the pattern to

oRegExp.Pattern = ".*Host Domain: .*\n"

 

by: traigoPosted on 2006-01-13 at 18:32:40ID: 15698171

It's been running now for about 15 min and hasn't made it through the first text file.

 

by: Idle_MindPosted on 2006-01-13 at 19:14:48ID: 15698308

There are two only two basic ways to delete a line from a text file:

    (1) Read the contents into memory.  Modify the contents in memory.  Overwite the file with the new contents.

    (2) Read the file line by line.  Echo only the desired lines to a secondary file.  Delete the original primary file.  Rename the secondary file to the primary file.

VB is very slow at string manipulation so method (1) is going to be slow with large files.  Try method (2) and see if it's any faster.

 

by: traigoPosted on 2006-01-13 at 19:18:28ID: 15698317

Ok, I killed it.  It was taking way too long.  I'll try #2.  Can you have 2 files open at the same time (1 for reading and 1 for writing)?

 

by: Idle_MindPosted on 2006-01-13 at 19:20:02ID: 15698324

Yes.

 

by: traigoPosted on 2006-01-13 at 19:21:34ID: 15698328

Thanks.  I'll work on it.  When I ran it without writing to a file, I was able to run through quickly.  So I think that writing each line to a new file as I pass the line should go quickly.  Thanks again for the help.

 

by: amit_gPosted on 2006-01-13 at 23:40:52ID: 15699076

I don't know what kind of machine you are running it at but I ran this on a file containing 100,000 lines and it completed in 3 seconds. I have a good machine but yours can't be that bad on any kind of machine. Also disk i/o is much slower compared to in memory comparision in any language. Thus reading and writing line by line would be much slower. Only when the RAM is running low, the in memory reading of file would translate to swap file writing and may cause the performace to degrade.

I noticed that the pattern still has an extra space in it. It should be

oRegExp.Pattern = ".*Host Domain:.*\n"

 

by: traigoPosted on 2006-01-14 at 00:11:46ID: 15699145

I went with this.  It works fine and takes less than a second to run through all my files.

Option Explicit

dim filepath, VBSName, objFSO, objTextFile, objTextFile2
dim fs, folder, file, item, line, fs1, filename

VBSname = wscript.scriptfullname

Filepath = left(VBSname, Len(VBSname) -(len(VBSname) - InstrRev(VBSname, "\")))

     set fs = CreateObject("Scripting.FileSystemObject")
     set folder = fs.GetFolder(FilePath)

     For each item in folder.Files
      If Right(item.name, 3) = "txt" Then

      Set objFSO = CreateObject("Scripting.FileSystemObject")
      Set objTextFile = objFSO.OpenTextFile (item, 1)
      Set fs1 = objFSO.CreateTextFile ("temp.txt",True)
      fs1.close
      Set objTextFile2 = objFSO.OpenTextFile ("temp.txt", 8)

      Do Until objTextFile.AtEndOfStream
          Line = objTextFile.ReadLine
            If InStr(1,Line, " Host Domain: ",1)  Then
            else
               objTextFile2.writeline line
            End If
      Loop

      set objTextFile = nothing
      set objTextFile2 = nothing

      filename = item.name

      objFSO.CopyFile "temp.txt", filename, true

      objFSO.DeleteFile "temp.txt"

      set objFSO = nothing
      Set fs1 = nothing

      End If
     next

msgbox "Done!"

 

by: amit_gPosted on 2006-01-14 at 00:19:05ID: 15699158

The ReadAll should also take about the same (acuallty less but you probably won't be able to notice). I have done similar things several times and ReadAll has always performed better than reading line by line. In any case it can't take 15 minutes and still be not over. Something else must have happened at that time due to which either the script ran so slow or for some reason it might have hanged.

 

by: Idle_MindPosted on 2006-01-14 at 07:22:15ID: 15700275

amit_g,

You are correct in saying that memory access is faster than hard drive access.

But vb is very slow at string manipulation.  If you use .ReadAll on a large file and then manipulate the resulting string, VB then has two make a copy in memory of the entire string.  Depending on what the system is doing this may take quite awhile.

Reading line by line may be slower for small files (and probably slower in general), but may make sense for larger files since it only has to deal with one line at a time.  It's a trade off...

 

by: amit_gPosted on 2006-01-14 at 11:16:40ID: 15701395

>>vb is very slow at string manipulation

Totally agree. I have done this in both ways (most of the time ReadAll) and I never had any problems either way. In this case also I feel the performace difference would not be measurable.

20120131-EE-VQP-002

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