#1391 Internal error #1 for dummy archive NUL

[frank]

Small nit about 7-Zip [64] 9.20 2010-11-18:

C:\Program Files\7-Zip> echo|7z a nul -tgzip -si -so>deleteme.gz
7-Zip [64] 9.20  Copyright (c) 1999-2010 Igor Pavlov  2010-11-18
Internal Error #1

C:\Program Files\7-Zip> echo|7z a . -tgzip -si -so>deleteme.gz
7-Zip [64] 9.20  Copyright (c) 1999-2010 Igor Pavlov  2010-11-18
Creating archive stdout
Everything is Ok

nul.gz instead of nul also results in internal error #1.
~~~~

[Igor Pavlov]

in your case you must use -an switch.
7z a nul ....
tries to open "nul" archive and update it with new data
MSDN:
Do not use the following reserved names for the name of a file:
CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9. Also avoid these names followed immediately by an extension; for example, NUL.txt is not recommended.

[frank]

The MSDN info is misleading: You cannot use NUL as the name for a "real" file under DOS, NT, or OS/2, because it is handled as alias of the NUL device. But if that is exactly what you want something like NUL.AVI (ffmpeg first pass), NUL.LST (unwanted assembler or compiler list), NUL.MAP (not planning to debug), etc. is handy.

Your a -an suggestion works, I'll use it instead of my shorter a . idea, thanks.