Scott Baker | 1fe7273 | 2019-10-21 10:58:51 -0700 | [diff] [blame] | 1 | // Copyright 2012 Jesse van den Kieboom. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | /* |
| 6 | Package flags provides an extensive command line option parser. |
| 7 | The flags package is similar in functionality to the go built-in flag package |
| 8 | but provides more options and uses reflection to provide a convenient and |
| 9 | succinct way of specifying command line options. |
| 10 | |
| 11 | |
| 12 | Supported features |
| 13 | |
| 14 | The following features are supported in go-flags: |
| 15 | |
| 16 | Options with short names (-v) |
| 17 | Options with long names (--verbose) |
| 18 | Options with and without arguments (bool v.s. other type) |
| 19 | Options with optional arguments and default values |
| 20 | Option default values from ENVIRONMENT_VARIABLES, including slice and map values |
| 21 | Multiple option groups each containing a set of options |
| 22 | Generate and print well-formatted help message |
| 23 | Passing remaining command line arguments after -- (optional) |
| 24 | Ignoring unknown command line options (optional) |
| 25 | Supports -I/usr/include -I=/usr/include -I /usr/include option argument specification |
| 26 | Supports multiple short options -aux |
| 27 | Supports all primitive go types (string, int{8..64}, uint{8..64}, float) |
| 28 | Supports same option multiple times (can store in slice or last option counts) |
| 29 | Supports maps |
| 30 | Supports function callbacks |
| 31 | Supports namespaces for (nested) option groups |
| 32 | |
| 33 | Additional features specific to Windows: |
| 34 | Options with short names (/v) |
| 35 | Options with long names (/verbose) |
| 36 | Windows-style options with arguments use a colon as the delimiter |
| 37 | Modify generated help message with Windows-style / options |
| 38 | Windows style options can be disabled at build time using the "forceposix" |
| 39 | build tag |
| 40 | |
| 41 | |
| 42 | Basic usage |
| 43 | |
| 44 | The flags package uses structs, reflection and struct field tags |
| 45 | to allow users to specify command line options. This results in very simple |
| 46 | and concise specification of your application options. For example: |
| 47 | |
| 48 | type Options struct { |
| 49 | Verbose []bool `short:"v" long:"verbose" description:"Show verbose debug information"` |
| 50 | } |
| 51 | |
| 52 | This specifies one option with a short name -v and a long name --verbose. |
| 53 | When either -v or --verbose is found on the command line, a 'true' value |
| 54 | will be appended to the Verbose field. e.g. when specifying -vvv, the |
| 55 | resulting value of Verbose will be {[true, true, true]}. |
| 56 | |
| 57 | Slice options work exactly the same as primitive type options, except that |
| 58 | whenever the option is encountered, a value is appended to the slice. |
| 59 | |
| 60 | Map options from string to primitive type are also supported. On the command |
| 61 | line, you specify the value for such an option as key:value. For example |
| 62 | |
| 63 | type Options struct { |
| 64 | AuthorInfo string[string] `short:"a"` |
| 65 | } |
| 66 | |
| 67 | Then, the AuthorInfo map can be filled with something like |
| 68 | -a name:Jesse -a "surname:van den Kieboom". |
| 69 | |
| 70 | Finally, for full control over the conversion between command line argument |
| 71 | values and options, user defined types can choose to implement the Marshaler |
| 72 | and Unmarshaler interfaces. |
| 73 | |
| 74 | |
| 75 | Available field tags |
| 76 | |
| 77 | The following is a list of tags for struct fields supported by go-flags: |
| 78 | |
| 79 | short: the short name of the option (single character) |
| 80 | long: the long name of the option |
| 81 | required: if non empty, makes the option required to appear on the command |
| 82 | line. If a required option is not present, the parser will |
| 83 | return ErrRequired (optional) |
| 84 | description: the description of the option (optional) |
| 85 | long-description: the long description of the option. Currently only |
| 86 | displayed in generated man pages (optional) |
| 87 | no-flag: if non-empty, this field is ignored as an option (optional) |
| 88 | |
| 89 | optional: if non-empty, makes the argument of the option optional. When an |
| 90 | argument is optional it can only be specified using |
| 91 | --option=argument (optional) |
| 92 | optional-value: the value of an optional option when the option occurs |
| 93 | without an argument. This tag can be specified multiple |
| 94 | times in the case of maps or slices (optional) |
| 95 | default: the default value of an option. This tag can be specified |
| 96 | multiple times in the case of slices or maps (optional) |
| 97 | default-mask: when specified, this value will be displayed in the help |
| 98 | instead of the actual default value. This is useful |
| 99 | mostly for hiding otherwise sensitive information from |
| 100 | showing up in the help. If default-mask takes the special |
| 101 | value "-", then no default value will be shown at all |
| 102 | (optional) |
| 103 | env: the default value of the option is overridden from the |
| 104 | specified environment variable, if one has been defined. |
| 105 | (optional) |
| 106 | env-delim: the 'env' default value from environment is split into |
| 107 | multiple values with the given delimiter string, use with |
| 108 | slices and maps (optional) |
| 109 | value-name: the name of the argument value (to be shown in the help) |
| 110 | (optional) |
| 111 | choice: limits the values for an option to a set of values. |
| 112 | This tag can be specified multiple times (optional) |
| 113 | hidden: if non-empty, the option is not visible in the help or man page. |
| 114 | |
| 115 | base: a base (radix) used to convert strings to integer values, the |
| 116 | default base is 10 (i.e. decimal) (optional) |
| 117 | |
| 118 | ini-name: the explicit ini option name (optional) |
| 119 | no-ini: if non-empty this field is ignored as an ini option |
| 120 | (optional) |
| 121 | |
| 122 | group: when specified on a struct field, makes the struct |
| 123 | field a separate group with the given name (optional) |
| 124 | namespace: when specified on a group struct field, the namespace |
| 125 | gets prepended to every option's long name and |
| 126 | subgroup's namespace of this group, separated by |
| 127 | the parser's namespace delimiter (optional) |
| 128 | command: when specified on a struct field, makes the struct |
| 129 | field a (sub)command with the given name (optional) |
| 130 | subcommands-optional: when specified on a command struct field, makes |
| 131 | any subcommands of that command optional (optional) |
| 132 | alias: when specified on a command struct field, adds the |
| 133 | specified name as an alias for the command. Can be |
| 134 | be specified multiple times to add more than one |
| 135 | alias (optional) |
| 136 | positional-args: when specified on a field with a struct type, |
| 137 | uses the fields of that struct to parse remaining |
| 138 | positional command line arguments into (in order |
| 139 | of the fields). If a field has a slice type, |
| 140 | then all remaining arguments will be added to it. |
| 141 | Positional arguments are optional by default, |
| 142 | unless the "required" tag is specified together |
| 143 | with the "positional-args" tag. The "required" tag |
| 144 | can also be set on the individual rest argument |
| 145 | fields, to require only the first N positional |
| 146 | arguments. If the "required" tag is set on the |
| 147 | rest arguments slice, then its value determines |
| 148 | the minimum amount of rest arguments that needs to |
| 149 | be provided (e.g. `required:"2"`) (optional) |
| 150 | positional-arg-name: used on a field in a positional argument struct; name |
| 151 | of the positional argument placeholder to be shown in |
| 152 | the help (optional) |
| 153 | |
| 154 | Either the `short:` tag or the `long:` must be specified to make the field eligible as an |
| 155 | option. |
| 156 | |
| 157 | |
| 158 | Option groups |
| 159 | |
| 160 | Option groups are a simple way to semantically separate your options. All |
| 161 | options in a particular group are shown together in the help under the name |
| 162 | of the group. Namespaces can be used to specify option long names more |
| 163 | precisely and emphasize the options affiliation to their group. |
| 164 | |
| 165 | There are currently three ways to specify option groups. |
| 166 | |
| 167 | 1. Use NewNamedParser specifying the various option groups. |
| 168 | 2. Use AddGroup to add a group to an existing parser. |
| 169 | 3. Add a struct field to the top-level options annotated with the |
| 170 | group:"group-name" tag. |
| 171 | |
| 172 | |
| 173 | |
| 174 | Commands |
| 175 | |
| 176 | The flags package also has basic support for commands. Commands are often |
| 177 | used in monolithic applications that support various commands or actions. |
| 178 | Take git for example, all of the add, commit, checkout, etc. are called |
| 179 | commands. Using commands you can easily separate multiple functions of your |
| 180 | application. |
| 181 | |
| 182 | There are currently two ways to specify a command. |
| 183 | |
| 184 | 1. Use AddCommand on an existing parser. |
| 185 | 2. Add a struct field to your options struct annotated with the |
| 186 | command:"command-name" tag. |
| 187 | |
| 188 | The most common, idiomatic way to implement commands is to define a global |
| 189 | parser instance and implement each command in a separate file. These |
| 190 | command files should define a go init function which calls AddCommand on |
| 191 | the global parser. |
| 192 | |
| 193 | When parsing ends and there is an active command and that command implements |
| 194 | the Commander interface, then its Execute method will be run with the |
| 195 | remaining command line arguments. |
| 196 | |
| 197 | Command structs can have options which become valid to parse after the |
| 198 | command has been specified on the command line, in addition to the options |
| 199 | of all the parent commands. I.e. considering a -v flag on the parser and an |
| 200 | add command, the following are equivalent: |
| 201 | |
| 202 | ./app -v add |
| 203 | ./app add -v |
| 204 | |
| 205 | However, if the -v flag is defined on the add command, then the first of |
| 206 | the two examples above would fail since the -v flag is not defined before |
| 207 | the add command. |
| 208 | |
| 209 | |
| 210 | Completion |
| 211 | |
| 212 | go-flags has builtin support to provide bash completion of flags, commands |
| 213 | and argument values. To use completion, the binary which uses go-flags |
| 214 | can be invoked in a special environment to list completion of the current |
| 215 | command line argument. It should be noted that this `executes` your application, |
| 216 | and it is up to the user to make sure there are no negative side effects (for |
| 217 | example from init functions). |
| 218 | |
| 219 | Setting the environment variable `GO_FLAGS_COMPLETION=1` enables completion |
| 220 | by replacing the argument parsing routine with the completion routine which |
| 221 | outputs completions for the passed arguments. The basic invocation to |
| 222 | complete a set of arguments is therefore: |
| 223 | |
| 224 | GO_FLAGS_COMPLETION=1 ./completion-example arg1 arg2 arg3 |
| 225 | |
| 226 | where `completion-example` is the binary, `arg1` and `arg2` are |
| 227 | the current arguments, and `arg3` (the last argument) is the argument |
| 228 | to be completed. If the GO_FLAGS_COMPLETION is set to "verbose", then |
| 229 | descriptions of possible completion items will also be shown, if there |
| 230 | are more than 1 completion items. |
| 231 | |
| 232 | To use this with bash completion, a simple file can be written which |
| 233 | calls the binary which supports go-flags completion: |
| 234 | |
| 235 | _completion_example() { |
| 236 | # All arguments except the first one |
| 237 | args=("${COMP_WORDS[@]:1:$COMP_CWORD}") |
| 238 | |
| 239 | # Only split on newlines |
| 240 | local IFS=$'\n' |
| 241 | |
| 242 | # Call completion (note that the first element of COMP_WORDS is |
| 243 | # the executable itself) |
| 244 | COMPREPLY=($(GO_FLAGS_COMPLETION=1 ${COMP_WORDS[0]} "${args[@]}")) |
| 245 | return 0 |
| 246 | } |
| 247 | |
| 248 | complete -F _completion_example completion-example |
| 249 | |
| 250 | Completion requires the parser option PassDoubleDash and is therefore enforced if the environment variable GO_FLAGS_COMPLETION is set. |
| 251 | |
| 252 | Customized completion for argument values is supported by implementing |
| 253 | the flags.Completer interface for the argument value type. An example |
| 254 | of a type which does so is the flags.Filename type, an alias of string |
| 255 | allowing simple filename completion. A slice or array argument value |
| 256 | whose element type implements flags.Completer will also be completed. |
| 257 | */ |
| 258 | package flags |