250 lines
8.5 KiB
Markdown
250 lines
8.5 KiB
Markdown
Getopt for Erlang
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=================
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Command-line parsing module that uses a syntax similar to that of GNU *getopt*.
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Requirements
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------------
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You should only need a somewhat recent version of Erlang/OTP, though the module
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has only been tested with Erlang R13B.
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Installation
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------------
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To compile the module you simply run ``make``.
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To run the unit tests run ``make test``.
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To run the example module run ``make example``.
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To build the (very) limited documentation run ``make doc``.
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Usage
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-----
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The *getopt* module provides four functions:
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parse([{Name, Short, Long, ArgSpec, Help}], Args :: string() | [string()]) ->
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{ok, {Options, NonOptionArgs}} | {error, {Reason, Data}}
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usage([{Name, Short, Long, ArgSpec, Help}], ProgramName :: string()) -> ok
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usage([{Name, Short, Long, ArgSpec, Help}], ProgramName :: string(),
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CmdLineTail :: string()) -> ok
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usage([{Name, Short, Long, ArgSpec, Help}], ProgramName :: string(),
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CmdLineTail :: string(), OptionsTail :: [{string(), string}]) -> ok
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The ``parse/2`` function receives a list of tuples with the command line option
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specifications. The type specification for the tuple is:
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-type arg_type() :: 'atom' | 'binary' | 'boolean' | 'float' | 'integer' | 'string'.
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-type arg_value() :: atom() | binary() | boolean() | float() | integer() | string().
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-type arg_spec() :: arg_type() | {arg_type(), arg_value()} | undefined.
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-type option_spec() :: {
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Name :: atom(),
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Short :: char() | undefined,
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Long :: string() | undefined,
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ArgSpec :: arg_spec(),
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Help :: string() | undefined
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}.
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The elements of the tuple are:
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- ``Name``: name of the option.
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- ``Short``: character for the short option (e.g. $i for -i).
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- ``Long``: string for the long option (e.g. "info" for --info).
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- ``ArgSpec``: data type and optional default value the argument will be converted to.
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- ``Help``: help message that is shown for the option when ``usage/2`` is called.
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e.g.
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{port, $p, "port", {integer, 5432}, "Database server port"}
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The second parameter receives the list of arguments as passed to the ``main/1``
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function in escripts or the unparsed command line as a string.
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If the function is successful parsing the command line arguments it will return
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a tuple containing the parsed options and the non-option arguments. The options
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will be represented by a list of key-value pairs with the ``Name`` of the
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option as *key* and the argument from the command line as *value*. If the option
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doesn't have an argument, only the atom corresponding to its ``Name`` will be
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added to the list of options. For the example given above we could get something
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like ``{port, 5432}``. The non-option arguments are just a list of strings with
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all the arguments that did not have corresponding options.
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e.g. For a program named ``ex.escript`` with the following option specifications:
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OptSpecList =
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[
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{host, $h, "host", {string, "localhost"}, "Database server host"},
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{port, $p, "port", integer, "Database server port"},
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{dbname, undefined, "dbname", {string, "users"}, "Database name"},
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{xml, $x, undefined, undefined, "Output data in XML"},
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{verbose, $v, "verbose", boolean, "List all the actions executed"},
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{file, undefined, undefined, string, "Output file"}
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].
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And this command line:
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Args = "-h myhost --port=1000 -x myfile.txt -v dummy1 dummy2"
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Which could also be passed in the format the ``main/1`` function receives the arguments in escripts:
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Args = ["-h", "myhost", "--port=1000", "-x", "file.txt", "-v", "dummy1", "dummy2"].
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The call to ``getopt:parse/2``:
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getopt:parse(OptSpecList, Args).
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Will return:
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{ok,{[{host,"myhost"},
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{port,1000},
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xml,
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{file,"file.txt"},
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{dbname,"users"},
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{verbose,true}],
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["dummy1","dummy2"]}}
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The other functions exported by the ``getopt`` module (``usage/2``, ``usage/3``
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and ``usage/4``) are used to show the command line syntax for the program.
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For example, given the above-mentioned option specifications, the call to
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``getopt:usage/2``:
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getopt:usage(OptSpecList, "ex1").
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Will show (on *stdout*):
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Usage: ex1 [-h <host>] [-p <port>] [--dbname <dbname>] [-x] [-v] <file>
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-h, --host Database server host
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-p, --port Database server port
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--dbname Database name
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-x Output data in XML
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-v List all the actions executed
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<file> Output file
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This call to ``getopt:usage/3`` will add a string after the usage command line:
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getopt:usage(OptSpecList, "ex1", "[var=value ...] [command ...]").
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Will show (on *stdout*):
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Usage: ex1 [-h <host>] [-p <port>] [--dbname <dbname>] [-x] [-v <verbose>] <file> [var=value ...] [command ...]
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-h, --host Database server host
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-p, --port Database server port
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--dbname Database name
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-x Output data in XML
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-v, --verbose List all the actions executed
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<file> Output file
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Whereas this call to ``getopt:usage/3`` will also add some lines to the options
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help text:
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getopt:usage(OptSpecList, "ex1", "[var=value ...] [command ...]",
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[{"var=value", "Variables that will affect the execution (e.g. debug=1)"},
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{"command", "Commands that will be executed (e.g. count)"}]).
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Will show (on *stdout*):
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Usage: ex1 [-h <host>] [-p <port>] [--dbname <dbname>] [-x] [-v <verbose>] <file> [var=value ...] [command ...]
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-h, --host Database server host
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-p, --port Database server port
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--dbname Database name
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-x Output data in XML
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-v, --verbose List all the actions executed
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<file> Output file
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var=value Variables that will affect the execution (e.g. debug=1)
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command Commands that will be executed (e.g. count)
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Command-line Syntax
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-------------------
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The syntax supported by the ``getopt`` module is very similar to that followed
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by GNU programs, which is described [here](http://www.gnu.org/s/libc/manual/html_node/Argument-Syntax.html).
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Options can have both short (single character) and long (string) option names.
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A short option can have the following syntax:
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-a Single option 'a', no argument or implicit boolean argument
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-a foo Single option 'a', argument "foo"
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-afoo Single option 'a', argument "foo"
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-abc Multiple options: 'a'; 'b'; 'c'
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-bcafoo Multiple options: 'b'; 'c'; 'a' with argument "foo"
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A long option can have the following syntax:
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--foo Single option 'foo', no argument
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--foo=bar Single option 'foo', argument "bar"
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--foo bar Single option 'foo', argument "bar"
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We can also have options with neither short nor long option name. In this case,
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the options will be taken according to their position in the option specification
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list passed to ``getopt:/parse2``.
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For example, with the following option specifications:
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OptSpecList =
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[
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{xml, $x, "xml", undefined, "Output data as XML"},
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{dbname, undefined, undefined, string, "Database name"},
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{output_file, undefined, undefined, string, "File where the data will be saved to"}
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].
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And these arguments:
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Args = "-x mydb file.out dummy1 dummy1".
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The call to ``getopt:parse/2``:
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getopt:parse(OptSpecList, Args).
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Will return:
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{ok,{[xml,{dbname,"mydb"},{output_file,"file.out"}],
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["dummy1","dummy1"]}}
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Finally, the string ``--`` is considered an option terminator (i.e. all
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arguments after it are considered non-option arguments) and the single ``-``
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character is considered as non-option argument too.
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Argument Types
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--------------
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The arguments allowed for options are: atom; binary; boolean; float; integer; string.
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The ``getopt`` module checks every argument to see if it can be converted to its
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correct type. In the case of boolean arguments, the following values (in lower or
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upper case) are considered ``true``:
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- true
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- t
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- yes
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- y
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- on
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- enabled
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- 1
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And these ones are considered ``false``:
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- false
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- f
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- no
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- n
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- off
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- disabled
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- 0
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