cliapp: Config file and option conventions for python command line framework

DESCRIPTION

cliapp is a Python programming framework for writing command line applications for Unix-like operating systems. This manual page describes the conventions for configuration files and command line parsing provided by cliapp.

Configuration file variables and command line options are handled by cliapp under a uniform abstraction: every setting is available both in configuration files and command line options. There are a few settings, provided by the framework itself, which are only available on the command line. For example, --help outputs a short help text, listing all the available options, and --dump-config outputs a list of current configuration settings.

Command line parsing follows GNU conventions: short options start with a single dash, long options with two dashes, and options may be used anywhere on the command line. The order of options versus non-options does not matter. The exception is some of the options provided by the framework, which are executed immediately when found, and may be prevent the rest of the options from being parsed. (--dump-config is one of these, so use it at the end of the command line only.) Use -- on the command line to signal the end of options: no arguments after that are considered to be option.

Some settings may have aliases, which can be only a single character, and in that case they're parsed as single-character option names.

Some applications have subcommands, which means that the first non-option argument is used to tell the application what to do. This is similar to what many version control systems do, for example CVS, svn, bzr, and git. Options are global, and are not specific to subcommands. Thus, --foo means the same thing, regardless of what subcommand is being used.

Configuration files

Configuration files use INI file syntax. All the settings are in the [config] section. Other sections are allowed, but it is up to the application to give meaning to them.

Multiple configuration files may be read. Settings from later ones override settings from earlier ones. Options override settings from the configuration files.

String list settings

Some settings may be a list of values (each value being a string). For example, there might be a setting for patterns to search for, and multiple patterns are allowed. On the command line, that happens by using the option multiple times. In the configuration file, all values are given on one line, separated by commas. This is a non-standard extension to the INI file syntax. There is no way to escape commas.

Example:

```
[config]
pattern = foo, bar, foobar
```

Boolean (true/false or on/off or yes/no) settings

When a setting can be either on or off, it's called a Boolean setting. Such settings are turned off by default, and turned on if used on the command line. In a configuration file, they need to be set to a value: if the value is one of yes, on, true, or the number 1, the setting is turned on. Any other value means it is turned off.

[config]
verbose = true
attack-kittens = no

This turns the verbose setting on, but does not launch attack kittens.

For every boolean setting, two command line options are added. If the setting is called foo, the option --foo will turn the setting on, and --no-foo will turn it off. The negation is only usable on the command line: its purpose is to allow the command line to override a setting from the configuration file.

Logging and log files

Programs using cliapp automatically support several options for configuring the Python logging module. See the --help output for options starting with log for details. Logging can happen to a file or the system log. Log files can be rotated automatically based on size.

The --trace option enables additional debug logging, which is usually only useful for programmers. The option configures the tracing library for Python, by Lars Wirzenius, which allows logging values of variables and other debug information in a way that is very lightweight when the tracing is turned off. The option specifies for which source code files to turn on tracing. The actual logging happens via the normal Python logging facilities, at the debug level.

Python profiling support

You can run the application under the Python profiler (cProfile) by setting an environment variable. The name of the variable is FOO_PROFILE, where FOO is the name of the program, as set by the application code or determined by cliapp automatically. The value of the environment variable is the name of the file to which the resulting profile is to be written.

Manual page generation

cliapp can generate parts of a manual page: the SYNOPSIS and OPTIONS sections. It fills these in automatically based on the subcommand and settings that a program supports. Use the --generate-manpage=FILE option, which is added automatically by cliapp. The FILE is a manual page marked up using the -man macros for troff(1). It should have empty SYNOPSIS and OPTIONS sections, and cliapp will fill them in. The output it to the standard output.

For example:

foo --generate-manpage=foo.1.in > foo.1

You would keep the source code for the manual page in foo.1.in and have your Makefile produce foo.1 as shown above.

Subcommands

cliapp provides a way for the application to have subcommands, in the style of git(1), for example. If the application is called foo, then it can have subcommands such as foo search, and foo print. The application gets to define the name and meaning of each subcommand. However, all settings (options and configuration files) are global, and can be used with all subcommands. It is up to each subcommand what settings it obeys.

If there are any subcommands, cliapp automatically adds the help subcommand. It allows you to get the help text for a specific subommand: foo help print, for example.

cliapp (5)