整个过程可以分为两步：
一、递归遍历目录；
二、逐个处理文件。
至于是否用到进制替换要看你的目的，要看“123123123sd”这个字符串的性质。
个人认为需要过滤下文件类型。例如TXT，HTML，INI，ASP，PHP ，JS等等这些类型的文件内容都是字符串性质。但是，读很多格式的复杂文件，要通过二进制流方式，那么读到的可能不是“123123123sd”这种形式。
以下是演示代码，仅供参考。
Option Explicit
Private FileCount As Long, lcount As Long '文件计数Private Sub Command1_Click()
DirFolder "E:\Web"
MsgBox "共扫描了" & FileCount & "个文件！找到了" & lcount & "行"
End Sub
Private Function DirFolder(FolderPath As String) As Long
On Error Resume Next
Dim FSO, F, Folder, MulitFolder, File, MulitFile, Path As String
Set FSO = CreateObject("Scripting.FileSystemObject")
Set F = FSO.GetFolder(FolderPath)
Set MulitFolder = F.SubFolders
For Each Folder In MulitFolder
Path = FolderPath & "\" & Folder.Name & "\"
Set MulitFile = Folder.files
For Each File In MulitFile '文件处理
If GetType(Path & File.Name) = "php" Then '文件类型过滤，
Me.Cls: Print "正在处理：" & Path & File.Name '显示
List1.AddItem Path & File.Name '加载到列表
FileCount = FileCount + 1 '文件计数
'**********此处添加文件处理函数*************
DealFlie Path & File.Name '自定义函数
'***********************************
End If
DoEvents
Next
Call DirFolder(FolderPath & "\" & Folder.Name) '递归调用
Next
End Function
'文件处理函数示例
Private Function DealFlie(FileName As String) As Long
Dim n As Integer, s As String
n = FreeFile()
Open FileName For Input As #n
While Not EOF(n)
Input #121, s
If InStr(s, "123123123sd") <> 0 Then
lcount = lcount + 1
End If
Wend
Close #n
End Function
'获取文件后缀
Private Function GetType(src As String) As String
Dim i As Long
For i = Len(src) To 1 Step -1
If Mid(src, i, 1) = "." Then Exit For
Next i
GetType = Mid(src, i + 1)
End Function