Useless tips?
This page shows some, er, let's call it "unexpected" behaviour of various DOS commands.Many will be of no practical use -- hence this page's title -- but it may be fun to experiment with them.
DOSKEY and SET /P
A tip by Padmanabha Holla:
If you have a doskey macro defined and if you input that
macro string as input for any SET /P varname= command,
later on varname contains the alias of your input, not your
input!
Thanks PadmanabhaC:\>DOSKEY fit=dirC:\>DOSKEY xla=clsC:\>SET /P Test=Macro1?Macro1?xlaC:\>ECHO %Test%cls C:\>SET /P Test=Macro2?Macro2?fitC:\>ECHO %Test%dir C:\>SET /P Test=Macro3?Macro3?DoesNotExistC:\>ECHO %Test%DoesNotExistC:\>
+ Prefix
Adding a plus sign before a command does some pretty weird things in DOS.Try this for example, and watch the path in your prompt:
C:\>+MD
C:\>+CD
C:\D>CD..
C:\>+RD
C:\>+CD
Directory not found
C:\>
+COPY C:
is interpreted as COPY Y C:+DIR will be interpreted as DIR RThe effect of the + before a DOS command is that the last character of the DOS command is inserted as the first command line argument.
This works for COMMAND.COM's "internal commands" only.
As I said, pretty weird and pretty useless.
Unless, of course, you are looking for a way to make your batch files hard to understand.
(Thanks for Günther Brunthaler for helping me work out a proper description of the effect).
ATTRIB
ATTRIB,Removes all attributes from all files in the current directory, like
ATTRIB *.* -S -H -R -AEscape Characters
Both NT and OS/2 offer the ˆ (caret) as an escape character for command lines. Both will display:Usage: ABC.BAT <drive:>ECHO Usage: ABC.BAT ˆ<drive:ˆ>The first time I heard about this strange behavior was in a post from Mark Stang in the alt.msdos.batch news group.
Let's take this simple batch file, for example:
SET DATE=ˆ
12/12/99
ECHO Date=%DATE%
Date=12/12/99DATE/T
command in another batch file, for example.In OS/2, however, the output from that same batch file looks like this:
Date=SET DATE will display:Date=
12/12/99
SET DATE| FIND /V "DATE="In NT, the caret at the end of the line is interpreted as "skip the following linefeed".
In OS/2, the SET command interprets the caret as an escape character for the following linefeed, so the variable will contain a linefeed. A pity it cannot be displayed using %variable%, that would have allowed multiple lines of text in a single variable.
Right now, in OS/2, the only use I could think of is for hiding variables.
If you did find any other way to use this "hidden feature", please send it to my e-mail address.
SET Quirk
Besides the "long list of known problems" with NT's SET /A switch, it has some "unknown" features too.I haven't found a useful application of the following features yet, maybe you can think of some.
These features were mailed to me by Ken Gould. Thanks.
The common way to use the /A switch is like this:
SET /A variable = mathematical expressionSET /A mathematical expressionSET /A 75 / 5An extra "bonus" feature is the way the result of the expression is displayed: without a carrige return/line feed!
Try this:
(SET /A 75 / 5) > TEST.TXTKen Gould also mailed me a trick to use when you do want a carriage return/line feed at the end:
(SET /A 75 / 5) | MORE > TEST.TXTIf you prefer internal commands, use this instead:
(SET /A 75 / 5) > TEST.TXT
ECHO.>> TEST.TXT
Don't, however, expect it to work in the following batch file:
SET /A %1 %2 %3 %4 %5 %6 %7 %8 %9SET /A %*12 + 3
will return nothing.This behaviour seems rather inconsitent.
What does work is this:
SET /A Result = %*
SET Result
This tip was shown to me by Chris Moore. Thanks.
ECHO
Robert Van Etta reported some very odd behaviour of the ECHO command in Windows 2000/XP/Server 2003. Type:ECHO ˆType in any text, followed by the Enter key, and it will be echoed again.
To store this text into a file, type:
> MYINPUT.TXT ECHO ˆCreate Empty Files
to create an empty (zero bytes) file I always used:TYPE NUL > new_empty_file_nameCD.> new_empty_file_name
