How can I determine if a file is locked using VBS? - vbscript

Question

I am writing a VB Script to update some files on the network. Before beginning, I want to know if any of the files are locked. I'd like to do this before I actually do any updates.
I am aware that I can handle the error if the file is locked when I try to replace it, but I really want to know if any files are locked before I start updating any files.
Is there any way to see that a file is locked using VBS (apart from trying to replace it)?

Answer 1

This function determines whether a file of interest can be accessed in 'write' mode. This is not exactly the same as determining whether a file is locked by a process. Still, you may find that it works for your situation. (At least until something better comes along.)
This function will indicate that 'write' access is not possible when a file is locked by another process. However, it cannot distinguish that condition from other conditions that prevent 'write' access. For instance, 'write' access is also not possible if a file has its read-only bit set or possesses restrictive NTFS permissions. All of these conditions will result in 'permission denied' when a 'write' access attempt is made.
Also note that if a file is locked by another process, the answer returned by this function is reliable only at the moment the function is executed. So, concurrency problems are possible.
An exception is thrown if any of these conditions are found: 'file not found', 'path not found', or 'illegal file name' ('bad file name or number').
Function IsWriteAccessible(sFilePath)
' Strategy: Attempt to open the specified file in 'append' mode.
' Does not appear to change the 'modified' date on the file.
' Works with binary files as well as text files.
' Only 'ForAppending' is needed here. Define these constants
' outside of this function if you need them elsewhere in
' your source file.
Const ForReading = 1, ForWriting = 2, ForAppending = 8
IsWriteAccessible = False
Dim oFso : Set oFso = CreateObject("Scripting.FileSystemObject")
On Error Resume Next
Dim nErr : nErr = 0
Dim sDesc : sDesc = ""
Dim oFile : Set oFile = oFso.OpenTextFile(sFilePath, ForAppending)
If Err.Number = 0 Then
oFile.Close
If Err Then
nErr = Err.Number
sDesc = Err.Description
Else
IsWriteAccessible = True
End if
Else
Select Case Err.Number
Case 70
' Permission denied because:
' - file is open by another process
' - read-only bit is set on file, *or*
' - NTFS Access Control List settings (ACLs) on file
' prevents access
Case Else
' 52 - Bad file name or number
' 53 - File not found
' 76 - Path not found
nErr = Err.Number
sDesc = Err.Description
End Select
End If
' The following two statements are superfluous. The VB6 garbage
' collector will free 'oFile' and 'oFso' when this function completes
' and they go out of scope. See Eric Lippert's article for more:
' http://blogs.msdn.com/b/ericlippert/archive/2004/04/28/when-are-you-required-to-set-objects-to-nothing.aspx
'Set oFile = Nothing
'Set oFso = Nothing
On Error GoTo 0
If nErr Then
Err.Raise nErr, , sDesc
End If
End Function

Answer 2

The script below tries to write to a file for 30 seconds and gives up after that. I needed this when all our users had to click on a script. Chances are that multiple users try to write at the same time. OpenCSV() tries to open the file 30 times with a delay of 1 second in between.
Const ForAppending = 8
currentDate = Year(Now) & "-" & Month(Now) & "-" & Day(Now) & " " & Hour(Now) & ":" & Minute(Now) & ":" & Second(Now)
filepath = "\\network\path\file.csv"
Set oCSV = OpenCSV( filepath )
oCSV.WriteLine( currentDate )
oCSV.Close
Function OpenCSV( path )
Set oFS = CreateObject( "Scripting.FileSystemObject" )
For i = 0 To 30
On Error Resume Next
Set oFile = oFS.OpenTextFile( path, ForAppending, True )
If Not Err.Number = 70 Then
Set OpenCSV = oFile
Exit For
End If
On Error Goto 0
Wscript.Sleep 1000
Next
Set oFS = Nothing
Set oFile = Nothing
If Err.Number = 70 Then
MsgBox "File " & filepath & " is locked and timeout was exceeded.", vbCritical
WScript.Quit
End If
End Function

Answer 3

Or, more simply:
Assuming you already have a variable in your VBS named FileName, which contains the full filepath you want to test:
Dim oFso, oFile
Set oFso = CreateObject("Scripting.FileSystemObject")
Set oFile = oFso.OpenTextFile(FileName, 8, True)
If Err.Number = 0 Then oFile.Close
Line 3 tries to open the file you want to test with append permissions enabled. e.g. it attempts to open the file with a write lock.
If opening the file with a write lock generates an error, then your VBS will error on the third line and not continue. At that point your error handling from wherever you called the VBS should kick in. The error message will be "Permission Denied" if you couldn't get a write lock.
If opening the file with a lock doesn't result in an error, then line 4 closes it again. You can now open the file or do whatever you want with it, confident that it doesn't have a write lock on it.