27) MULTIPLE DOS COMMANDS ON ONE LINE

    set &=%4&|set n$=%4|set m$=%3|set #=%2|set !=%0 
            /|\       /|\       /|\      /|\ 
             |_________|_________|________|_________________________Separators


    The separators (|) used in the line, are these doing anything
    other than separating commands?  Can this be used for entering multiple
    commands on any line in a batch file regardless of type of command?

                              Peter Joynson

    I believe you are right about this, but I think it pipes any output from
    the previous command to the next one (your example doesn't have any
    output.  For example: ECHO Y|ERASE *.*  This would pipe the Y to the
    command ERASE *.* so you wouldn't have to enter the Y for the "Are you
    sure" prompt.

                              Robert Hupf

    The | is a pipe symbol, well documented in your DOS manual.  (Read it
    before you read the rest of this message if you don't know about
    pipes already, otherwise the rest won't make sense.)  Pipes can be
    used to put multiple commands on a single line, provided that the
    first command does not write anything to StdOout which might cause a
    problem when read by the second command as StdIn. Also, it is assumed
    that you don't want to see the output of any but the last command,
    since each command's output will be piped to the next's input.  Note
    that in this case SET neither writes anything to StdOut nor reads
    StdIn.  Thirdly, you must have write access to the current drive, or
    %temp% if defined, since a pipe always creates a temporary file.  Eg
    this would not work if run from a write protected floppy (unless
    %temp% was defined), since DOS would fail to create the temporary
    files.

    Pipes create temporary files even if no actual data is sent to
    StdOut because Command effectively treats this:

            prog1 | prog2

    as something like this:

            prog1 > %temp%tempfile
            prog2 < %temp%tempfile
            del %temp%tempfile

    Even if prog1 doesn't create any output, at least one zero length
    file is created.  To demonstrate, try this

            set temp=
            set | dir

    I must say this beats the usual boring old "how do I echo a blank
    line in a batch file" etc.

                              Mitch Ames

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28) COM or EXE

    Also, have you noticed that 4DOS.COM (when viewed with LIST) begins
    with the letters "MZ"?  Isn't that the mark of a .EXE file?  Very
    interesting...

                              Thomas Smith

    It sure is, and that's an example of something else that may be
    a MUF.  DOS doesn't care whether the extension on an executable
    file is .COM or .EXE.  It looks at the beginning of the file and
    does the right thing according to what it finds.

                              Gary Smith

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