batman

楼主自己对着改：

@echo off
(for /f "delims=" %%a in (a.txt) do if not defined "%%a" echo %%a&set ""%%a"=a")>b.txt
start b.txt
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batman

还是一个不通用的解：

@echo off
for /f "delims=" %%a in (a.txt) do set /a "_%%a+=1"
(for /f "tokens=1,2 delims==_" %%a in ('set _') do if %%b equ 1 echo %%a)>b.txt
start b.txt
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batman

@echo off&setlocal enabledelayedexpansion
rem 每行字符间不能有空格,;><&tab以及成对的!字符
set "str= "
for /f "delims=" %%a in (a.txt) do (  
  if "!str: %%a =!" neq "!str!" (
    set "str=!str: %%a =!"
    ) else (
    set "str=!str! %%a "
  )
)   
(for %%a in (%str%) do echo %%a)>b.txt
start b.txt
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batman

vbs的，应该很通用了：

Set fso = CreateObject("scripting.filesystemobject")
vbstr = fso.OpenTextFile("a.txt").ReadAll()
arr = Split(vbstr, vbCrLf)
For Each str In arr
  If InStr(vbout, str) = 0 Then
    vbout = vbout & str & vbCrLf
    Else
    vbout = Replace(vbout, str, "$@#^&><")
  End If
Next
fso.OpenTextFile("b.txt", 2, True).Write Replace(vbout, "$@#^&><" & vbCrLf, "")
MsgBox "ok"
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