Trouble with InStr - Shadow-Copy Script with logging and error check

Question

I am trying to develop a VBS script which creates backups with shadowcopy.exe and copies them with rsync to a specific destination. There are log files which will be created for the rsync copy procedure by the same script and getting checked for specific words (like "error" or "failed").

The problem I have now is that I don't know how to check the log files/read out the specific keywords.

I read that InStr is a possibility to solve my problem, but I dont't know how to use it to define my keywords, read them out and combine it with my mail alert. Maybe someone has an advice for me?

My code so far:

Dim oEmail, oConf
Dim authuser, authpass, smtpserver
Dim recipient,sender,subject,message 
Dim ObjFso
Dim FIL_LOG
Dim response

'Angaben zur Quelle und Ziel 
quelle = "c:\vshadow"   'beispiel c:\vshadow
ziel = "/cygdrive/c/users/example/desktop/test/"    'beispiel /cygdrive/c/users/example/desktop/test/

'angaben zu den emails die verschickt werden wollen
authuser = "example@example.de"
authpass = "123"
smtpserver = "server" 
recipient = "example@example.de"
sender = "rsync@test.de"
subject = "Test E-Mail"
message1 = "Schattenkopie konnte nicht erstellt werden"
message2 = "rsync befehl ist durchgelaufen"
message3 = "rsync ist abgebrochen"

'für den email versand benötigte daten
Set oEmail = CreateObject("CDO.Message")
Set oConf = CreateObject("CDO.Configuration")

oConf.Fields("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2
oConf.Fields("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = 25
oConf.Fields("http://schemas.microsoft.com/cdo/configuration/smtpserver") = smtpserver
oConf.Fields("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate") = 1
oConf.Fields("http://schemas.microsoft.com/cdo/configuration/sendusername") = authuser
oConf.Fields("http://schemas.microsoft.com/cdo/configuration/sendpassword") = authpass
oConf.Fields.Update 

'Schattenkopie erstellen
Const CONTEXT = "ClientAccessible"

Set Args = WScript.Arguments
If Args.Count() > 0 Then
     VOLUME = Args.item(0)
Else
     VOLUME = "C:\"
End If

Set objWMIService = GetObject("winmgmts:{impersonationLevel=impersonate}!\\.\root\cimv2")
Set objShadowStorage = objWMIService.Get("Win32_ShadowCopy")

errResult = objShadowStorage.Create(VOLUME, CONTEXT, strShadowID)

'falls schattenkopie nicht erstellt werden kann email mit Fehlermeldung, sonst gehts
'weiter
If errResult <> 0 Then
    oEmail.Configuration = oConf
    oEmail.To = recipient
    oEmail.From = sender
    oEmail.ReplyTo = sender
    oEmail.Subject = subject 
    oEmail.HTMLBody = message1
End If

'Mounted die Schattenkopie und Kopiert per Rsync
Set WshShell = WScript.CreateObject("WScript.Shell") 

WshShell.Run "%COMSPEC% /C ShadowSpawn.exe " & quelle & _
    " t: rsync -rltDv --log-file=rsync.log--link-dest=/" & ziel & _
    "/%last_run% /cygdrive/t/* " & ziel & _
    " > c:\users\example\desktop\vbs\rsync\bin\vss1.log ", 0, True

'''''''''''''''''''''
'Hier möchte ich die gerade erstelle log Datei auf Stichwörter wie z.B error
'untersuchen. Falls error in der log datei vorhanden ist soll es mir eine Abbruch
'mail schicken. Ansonsten eine email das alles gut durchgelaufen ist

ergenbis = InStr(1, vss1, error, 1)

'If Ergebnis <> 0 Then  'Email verschicken das alles durchgelaufen ist
    oEmail.Configuration = oConf
    oEmail.To = recipient
    oEmail.From = sender
    oEmail.ReplyTo = sender
    oEmail.Subject = subject 
    oEmail.HTMLBody = message2
Else   'abbruchmail verschicken
    oEmail.Configuration = oConf
    oEmail.To = recipient
    oEmail.From = sender
    oEmail.ReplyTo = sender
    oEmail.Subject = subject 
    oEmail.HTMLBody = message3
End If

oEmail.Send

Set oConf = Nothing
Set oEmail = Nothing

Answer 1

Use Option Explicit to avoid blunders like

ergenbis = instr(1, vss1, error, 1)
if Ergebnis <> 0 then  'Email verschicken das alles durchgelaufen ist

Think about the difference between name (variable, file) and content (variable, file).

Write a simple test script that applies InStr() to a file/each line of a file