Module subcmd

Handle subcommands and their parameters.

Subcommands are putting main command into different modes of operation. Main commands with subcommands are typical of package managers, version control systems, etc. This module provides a handler to conveniently load subcommands on demand, and parser to extract and route parameters to them from the command line.

The command line interface consists of having subcommand a free parameter, and a special collector-option to collect parameters for the subcommand:

   $ cmd -a -b -c \  # command and any usual options
         subcmd \    # subcommand
         -s foo \    # subcommand parameter 'foo', without value (flag)
         -s bar:xyz  # subcommand parameter 'bar', with the value 'xyz'

where -s is the collector-option, repeated for as many subcommand parameters as needed. The collector-option can be freely positioned in the command line, before or after the subcommand name, and mixed with other options.

The format of subcommand parameter is either param for flag parameters, param:value for parameters taking a value, or param:value1,value2,... for parameters taking a list of values. Instead of, or in addition to using comma-separated string to represent the list, some parameters can be repeated on the command line, and all the values collected to make the list.

Several subcommands may be given too, in which case a each subcommand parameter is routed to every subcommand which expects it. This means that all those subcommands should place the same semantics into the same-named parameter they are using.