-si (read data from stdin) switch
Causes 7-Zip to read data from stdin (standard input) instead of from disc files.
- Specifies a name that will be stored in the archive for the compressed data. If file_name is not specified, data will be stored without a name.
Note: The current version of 7-Zip does not support reading of archives from stdin.
7z a archive.gz -tgzip -siDoc2.txt < Doc.txt
compresses input stream from file Doc.txt to archive.gz archive using Doc2.txt file name.