Add getopts plugin README.

plugins/getopts/README.markdown

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+# getopts
+> friendly [`getopts`](http://en.wikipedia.org/wiki/Getopts) for [fish](https://fishshell.com) :fish:
+
+## Install
+
+```fish
+git clone https://github.com/bucaran/getopts
+mv getopts/getopts.fish custom/functions/path
+```
+
+## Tests
+
+Tests are implemented via [Oh-My-Fish](https://github.com/bpinto/oh-my-fish) spec runner _fish-spec_.
+
+## Premise
+Every utility / function needs to handle arguments. What usually happens is that every function does all the grunt work to parse `$argv` itself, and while some patterns do tend to recur, it's different almost every time. Enter fish `getopts`.
+
+## Synopsis
+  `getopts <option string> [ARGV...]`
+
+## Options
+#### `<option string> [:][<letter>][[:]<word>[:[^]]]`
+
+A string containing the option characters recognized by the utility calling `getopts`. If a `<letter>` or `<word>` ends in `:`, the option is expected to have an argument, which may be supplied separately or next to the option without spaces in the same string.
+
+To indicate long options: `<letter>:<word>` and `<word>` are both valid option strings that will attempt to match `-<letter>` and `--<word>`.
+
+To indicate _only_ short options, do not specify a `:<word>` after `<letter>`. For example, `a b` will match `-a` or `-b`.
+
+To indicate optional arguments, use a `^` character after a `:` at the end of the option in the option string. For example `<letter>:^` and `<letter>:<word>:^` are both valid. Optional arguments should be supplied in the same string as the option and without spaces, e.g, `-<letter>value` will correctly assign `value` as the argument to the the option `<letter>`, but `-<letter>` value, will parse `value` as the next argument in `<ARGV>`.
+
+To specify optional arguments using the option's long form, use a `=` character after the option: `--<word>=value`.
+
+Use a `:` at the beginning of the option string to enable strict mode. If enabled, `getopts` will exit with a status __> 0__ if or when an unknown option is found. See [Diagnostics](#diagnostics).
+
+#### `<ARGV>`
+
+List of options and operands to parse. `getopts` prints any matched options as well as available argument separated by a \n to stdout and returns with a status of __0__ if there are still arguments; else returns with a status __> 0__ if the end of the options is reached or an error occurs. See [Diagnostics](#diagnostics).
+
+#### Summary
+
+| Option String          |  Argument     | Short Style     | Long Style   |
+|:---------------:|:--------------:|------------------|:--------------------:|
+   `"q:qqq:"`          | Required   | `-q1` `-q 1`    | `--qqq 1`           |
+   `"q:qqq:^"`         | Optional    | `-q1`              | `--qqq=3`              |
+
+
+## Description
+`getopts` obtains options and their arguments from a list of parameters that, as indicated by <option string>, are single letters preceded by a `-` or words preceded by `--` and possibly followed by an argument value.
+
+fish `getopts` follows the specifications described in the [Utility Syntax Guidelines](http://pubs.opengroup.org/onlinepubs/7908799/xbd/utilconv.html). The following is a summary of the features:
+
++ Short options; single letters preceded by `-`, and long options; words preceded by `--`, are both supported.
+
++ Single letters may be grouped. `-abc` → `-a -b -c`
+
++ Options required to take an argument can specify the argument either in the same string as the option or separated from the by a space. (1) `-a argument`, (2) `-aargument`
+
++ Options that can take an argument optionally shall specify the argument in the same string as the option argument if in short option style: `-aargument`, or separated by a `=` if in long form: `--long-form=argument`. If a blank space is used, the following argument will be treated independently.
+
++ Options can appear multiple times in the same argument list. `getopts` will print every match sequentally on each call, and should default to the short form of the option if available.
+
++ The option delimiter `:` and optional argument character `^` shall not be used as an option.
+
++ `getopts` will return the remaining operands when the end of the options is reached, i.e, a `--` argument that is not an option is found, or an argument that does not begin with `-` is found.
+
+## Environment Variables
+The following environment variables are used internally by `getopts`. These variables are erased from memory when the function returns 1.
+
++ `__getopts_optstr` _Whitespace trimmed option string._
+
++ `__getopts_argv` _Preprocessed copy of arguments._
+
++ `__getopts_index` _Index of the next argument to handle._
+
++ `__getopts_required` _List of options with required arguments._
+
++ `__getopts_optional` _List of options with optional arguments._
+
+
+## <a name="diagnostics"></a>Diagnostics
+Possible exit status values are:
+
++ __0__: An argument formed like an option was found. This causes getopts to print the option short-style and its argument if avaiable. If strict-mode is enabled setting the first character of the option to `:`, an unknown option will cause `getopts` to fail. See below.
+
++ __1__: The end of the options was reached. Remaining operands are also sent to stdout.
+
++ __2__: An option argument was missing.
+
++ __3__: An unknown option was found. Only if strict-mode is enabled.
+
+## Examples
+```fish
+  function my_utility
+    while set optarg (getopts "l:long x: o:optional:^" $argv)
+      switch $optarg[1]
+        case l
+          echo handle `-l --long`
+        case x
+          echo handle `-x` w/ argument `$optarg[2]`
+        case o
+          echo handle `-o --optional` w/ optional argument `$optarg[2]`
+        case \*
+          echo unknown option `$optarg[1]`
+      end
+    end
+    echo -n operands: "`$optarg`"
+  end
+```
+
+## Links
++ [UNIX Utility Conventions](http://pubs.opengroup.org/onlinepubs/7908799/xbd/utilconv.html)
+
+## License
+[MIT](http://opensource.org/licenses/MIT) © [Jorge Bucaran](http://bucaran.me)