Sorry to be late on my own question. With the nightly of swift now which is available in docker swift includes format as a subcommand also on linux.
# Just do not use the -! swift format -h OVERVIEW: Format or lint Swift source code USAGE: swift-format [--version] <subcommand> OPTIONS: -v, --version Print the version and exit -h, --help Show help information. SUBCOMMANDS: dump-configuration Dump the default configuration in JSON format to standard output format (default) Format Swift source code lint Diagnose style issues in Swift source code See 'swift-format help <subcommand>' for detailed help. But the weird thing is that it is not listed as a sub command of the swift main command. This seams a bug?
swift -h ... Subcommands: swift build Build Swift packages swift package Create and work on packages swift run Run a program from a package swift test Run package tests swift repl Experiment with Swift code interactively Use `swift --version` for Swift version information. Use `swift --help` for descriptions of available options and flags. Use `swift help <subcommand>` for more information about a subcommand.