for /f "delims=" %%i in (a.txt) do (
    if not defined %%i set %%i=A & echo %%i>>aa.txt)
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(for /f "delims=" %%i in (a.txt) do (
    if not defined %%i set %%i=A
    echo %%i
))>>aa.txt
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(for /f "delims=" %%i in (a.txt) do (
    if not defined %%i set %%i=A
    echo.%%i
))>>aa.txt
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Const adOpenStatic = 3
Const adLockOptimistic = 3
Const adCmdText = &H0001 
Set objConnection = CreateObject("ADODB.Connection")
Set objRecordSet = CreateObject("ADODB.Recordset")

strPathToTextFile = "C:\"
strFile = "test.txt"

objConnection.Open "Provider=Microsoft.Jet.OLEDB.4.0;" & _
    "Data Source=" & strPathtoTextFile & ";" & _
    "Extended Properties=""text;HDR=NO;FMT=Delimited"""

objRecordSet.Open "Select DISTINCT * FROM " & strFile, _
objConnection, adOpenStatic, adLockOptimistic, adCmdText

Do Until objRecordSet.EOF
    WScript.Echo objRecordSet.Fields.Item(0).Value
    objRecordSet.MoveNext
Loop
objRecordSet.Close
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@ECHO OFF
Setlocal enableDelayedExpansion
for /f "tokens=*" %%i in (a.txt) do (
	for /f "tokens=*" %%j in ('findstr "%%i" a.txt')
		set /a a+=1
		if !a! geq 2 echo %%i>>aa.txt
)
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@echo off
sort test.txt /o tmp.txt
for /f "delims=" %%a in (tmp.txt) do (
   set "str=%%a"
   setlocal enabledelayedexpansion
   if not !str!==!last! echo %%a
   endlocal
   set "last=%%a"
)
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gawk "{a[$0]++}END{for(i in a)print i}" c:\test.txt
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gawk "{a[$0]++;if(a[$0]==1)print $0}" c:\test.txt
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