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Posted 14 Jan 2004

Tail utility for windows

, 18 Jan 2004
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Tail utility for windows


This simple program imitates the unix "tail -f" utility on windows.

Source code and Demo

The submitted source code contains one main file: Tail.cs. This is the core of the tail program. This file is used in two wrappers - a GUI wrapper and a CUI wrapper. The two projects in the solution illustrate using Tail.cs in a windows form application and a console application.

Code Walkthrough

.NET introduced the FileSystemWatcher, which is the main component of this program. By configuring this component one can listen to file system changes.

I first check whether the file exists. If it does exist then I monitor any changes to the file thus:

fileSystemWatcher.Changed += new FileSystemEventHandler(TargetFile_Changed);

If it does not exist yet, then I wait until the file is created before watching for file change notifications:

fileSystemWatcher.Created += new FileSystemEventHandler(TargetFile_Created);

When a change is made to the file, the method below gets the notification

public void TargetFile_Changed(object source, FileSystemEventArgs e)
 lock (this)
  byte[] bytesRead = new byte[maxBytes];
  FileStream fs = new FileStream(this.filename, FileMode.Open);
  if (fs.Length > maxBytes)
   this.previousSeekPosition = fs.Length - maxBytes;
  this.previousSeekPosition = (int)fs.Seek(
      this.previousSeekPosition, SeekOrigin.Begin);
  int numBytes = fs.Read(bytesRead, 0, maxBytes);
  this.previousSeekPosition += numBytes;

  StringBuilder sb = new StringBuilder();
  for (int i=0; i<numBytes; i++)

  this.MoreData(this, sb.ToString());

Within this, I ensure that the last characters are read in a large file which is longer than the number of characters that can be read. I then read the last set of characters starting from where we left off the previous time. The string of new characters is then sent to all listeners.

The sample programs listen to this notfication and then updates its user interface.


I have noticed an occasional exception saying that the target file is being accessed by another program. In the environment that I am working in, the target file is not always opened for writing, so I am able to get away with the above code for now. If it works, don't touch it uh. :-) But you feel free to correct it and post changes.

Bug Fixes

  • Added fix for file access exception. Thanks to Gary a.k.a garythom_work for this fix. (see thread below) - 17 Jan 2004


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

France France

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Comments and Discussions

QuestionCross-thread operation not valid Pin
TinyTony_16-Oct-13 0:05
memberTinyTony_16-Oct-13 0:05 
BugWell, this definitely does not work Pin
Zacky Pickholz20-Nov-12 8:05
memberZacky Pickholz20-Nov-12 8:05 
GeneralSlower than native code... Pin
therearefartoomanybens10-Mar-09 11:56
membertherearefartoomanybens10-Mar-09 11:56 
GeneralRe: Slower than native code... Pin
DEGT24-Sep-09 1:14
memberDEGT24-Sep-09 1:14 
GeneralNice little utility Pin
rc_cohn10-Nov-05 12:11
memberrc_cohn10-Nov-05 12:11 
GeneralSome text editors does not trigger fileSystemWatcher.Changed event! Pin
Tomer Shalev3-Aug-05 7:32
memberTomer Shalev3-Aug-05 7:32 
GeneralRe: Some text editors does not trigger fileSystemWatcher.Changed event! Pin
meraydin2-Dec-05 6:51
membermeraydin2-Dec-05 6:51 
GeneralUse in threads Pin
bollwerj24-May-04 8:11
memberbollwerj24-May-04 8:11 
GeneralRe: Use in threads Pin
DEGT24-Sep-09 1:36
memberDEGT24-Sep-09 1:36 
GeneralCall to TargetFile_Changed Pin
bollwerj28-Apr-04 9:41
memberbollwerj28-Apr-04 9:41 
GeneralRe: Call to TargetFile_Changed Pin
SathishVJ28-Apr-04 18:38
memberSathishVJ28-Apr-04 18:38 
GeneralRe: Call to TargetFile_Changed Pin
bollwerj30-Apr-04 3:55
memberbollwerj30-Apr-04 3:55 
GeneralRe: Call to TargetFile_Changed Pin
bollwerj3-May-04 2:38
memberbollwerj3-May-04 2:38 
GeneralAn Alternative Pin
Gary Brewer14-Feb-04 5:13
memberGary Brewer14-Feb-04 5:13 
GeneralTraceTool and Tail windows Pin
Thierry Parent19-Jan-04 20:59
memberThierry Parent19-Jan-04 20:59 
GeneralFree SFU 3.5 Pin
Anonymous19-Jan-04 7:40
memberAnonymous19-Jan-04 7:40 
Questionwhat does tail -f do? Pin
peterchen19-Jan-04 1:46
memberpeterchen19-Jan-04 1:46 
AnswerRe: what does tail -f do? Pin
SathishVJ20-Jan-04 3:34
memberSathishVJ20-Jan-04 3:34 
GeneralThows an Exception Pin
garythom_work15-Jan-04 5:03
membergarythom_work15-Jan-04 5:03 
GeneralRe: Thows an Exception Pin
SathishVJ20-Jan-04 3:27
memberSathishVJ20-Jan-04 3:27 

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