Option Base 1
Option Explicit
Option Private Module
'====================================================================================================
' Need to Add to Reference library Microsoft VBScript Regular Expressions 5.5
' File "vbscript.dll\3" in Folder "C:\Windows\System32\"
'====================================================================================================
Sub Test()
Dim RE As New RegExp
Dim x, tx$

tx = "=ИНДЕКС([1.xlsm]лист1!A1:D8;2;3)/МАКС([звезда.xlsm]свод1!K11:K22)"

RE.Global = True
RE.Pattern = "\[.+?\]"      ' The_Prist
For Each x In RE.Execute(tx)
    Debug.Print "The_Prist", x
Next x

RE.Pattern = "\[[^[]+\]"    ' Igor Goncharenko
For Each x In RE.Execute(tx)
    Debug.Print "IgGonch", x
Next x

RE.Pattern = "\w*.xlsm"     ' bigorq
For Each x In RE.Execute(tx)
    Debug.Print "bigorq", x
Next x

x = tx: If TextBetweenSeps(x, "[", "]", True) Then MsgBox Join(x, vbLf)
End Sub
'====================================================================================================
' https://www.planetaexcel.ru/forum/index.php?PAGE_NAME=message&FID=1&TID=78513&TITLE_SEO=78513-izvlecheniya-dannykh-iz-skobok
Function TextBetweenSeps(tmp, delL$, delR$, MsgFalse As Boolean) As Boolean ' получаем массив элементов из разделителей
Dim arrOut(), i&
Dim lPos&, rPos&, lLen&, rLen&

lLen = Len(delL): rLen = Len(delR): rPos = -rLen + 1
ReDim arrOut(Len(tmp) \ 2)
    Do
        lPos = InStr(rPos + rLen, tmp, delL)
        If lPos = 0 Then Exit Do

        rPos = InStr(lPos + lLen, tmp, delR)
        If rPos = 0 Then Exit Do

        i = i + 1: arrOut(i) = Mid$(tmp, lPos + lLen, rPos - lPos - lLen)
    Loop

    If i = 0 Then
        If MsgFalse Then MsgBox "В строке «" & tmp & "» значения между разделителями «" & delL & "» и «" & delR & "» — НЕ НАЙДЕНЫ!", vbCritical, "Text_Betweenseps"
        Exit Function
    End If
ReDim Preserve arrOut(i): tmp = arrOut: TextBetweenSeps = True
End Function
'====================================================================================================