Is file path needed in (Shell Function) VBA? - shell

Question

I have a Matlab-generated executable file, Myfile.exe to call from excel-vba. I learned (Shell Function) is what I need to use.
I don't want to include the whole file path as I do not want to restrict the user to a certain folder in a certain location on each computer.
I have the following code to call the executable, which works fine:
Sub MyExe()
On Error Resume Next
Shell ("C:\Users\elwany\Desktop\Myfolder\Myfile.exe")
If Err <> 0 Then
MsgBox "Can't start the application.", vbCritical, "Error"
End If
End Sub
My problem/question is
I put the executable + the Excel file with the VBA project in the same folder (Myfolder), and then I modify the code to:
Sub MyExe()
On Error Resume Next
Shell ("Myfile.exe")
If Err <> 0 Then
MsgBox "Can't start the application.", vbCritical, "Error"
End If
End Sub
Sometimes it works, sometimes it doesn't!
For example, yesterday I ran the VBA code, it worked. Today I opened the same Excel file, same folder, same everything, it gives "Can't Start Application" error msg!!
Is it not okay to remove the file path even if I have everything in one folder?
Why does it sometimes work, sometimes not?
Is adding the file path absolutely mandatory?

Answer 1

As you have enquire further about different directories note that you can either
Use ChDir as per my earlier comment to your question
Use Dir instead to validate that myfile.exe is where it needs to be. This method doesn't need error handling to handle the file being missing.
Sub TestB()
Dim strPath As String
strPath = Dir("c:\temp\myfile.exe")
If Len(strPath) > 0 Then
Shell strPath
Else
MsgBox "Path doesn't exist"
End If
End Sub
Sub TestA()
On Error Resume Next
'use the host workbook path
' ChDir ThisWorkbook.Path
'set path here
ChDir "C:\temp"
Shell ("Myfile.exe")
If Err <> 0 Then
MsgBox "Can't start the application.", vbCritical, "Error"
Else
MsgBox "sucess!", vbOKOnly
End If
End Sub

Answer 2

When you run a shell like this without a path specified it runs from the Active Directory. What the Active Directory is depends on the OS, not Excel/VBA (unless you explicitly set it)
Try this instead
Sub MyExe()
On Error Resume Next
Shell (ThisWorkbook.Path & "\Myfile.exe")
If Err <> 0 Then
MsgBox "Can't start the application.", vbCritical, "Error"
End If
End Sub