What does :: (double colon) mean in DOS batch files?

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:: is a label (inaccurately also known as comment label) can be, in practice, considered a comment just as REM is, because it is an “un-goto-able” label.

There are some differences between REM and ::, though. The main ones are:

  • With ECHO ON a REM line is shown but not a line commented with ::

  • A :: can execute a line end caret (that is, a ^ at the end of a line starting with :: makes the next line also a comment):

     :: This is a comment^
 echo but watch out because this line is a comment too

  • Labels and :: have a special logic and can cause problems in parentheses blocks – take care when using them inside ( ). Example:

     for %%D in (hi) do (
     echo Before...
     :: My comment
     :: Some other comment
     echo After...
 )

    Outputs:

     Before ...
 The system cannot find the drive specified.
 After...

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