package.json 中的scripts的脚本 中--这符号表示啥意思

Question

这里面的--表示啥意思

Answer 1

命令的参数，比如webpack --config webpack.config.js表示webpack的config参数的值为webpack.config.js。

但是并不是所有的命令参数都是这个格式，详细可以查看该命令的文档。

以webpack为例

webpack-cli 3.3.8

Usage: webpack-cli [options]
       webpack-cli [options] --entry <entry> --output <output>
       webpack-cli [options] <entries...> --output <output>
       webpack-cli <command> [options]

For more information, see https://webpack.js.org/api/cli/.

Config options:
  --config               Path to the config file
                         [string] [default: webpack.config.js or webpackfile.js]
  --config-register, -r  Preload one or more modules before loading the webpack
                         configuration      [array] [default: module id or path]
  --config-name          Name of the config to use                      [string]
  --env                  Environment passed to the config, when it is a function
  --mode                 Enable production optimizations or development hints.
                                  [choices: "development", "production", "none"]

Basic options:
  --context    The base directory (absolute path!) for resolving the `entry`
               option. If `output.pathinfo` is set, the included pathinfo is
               shortened to this directory.
                                       [string] [default: The current directory]
  --entry      The entry point(s) of the compilation.                   [string]
  --watch, -w  Enter watch mode, which rebuilds on file change.        [boolean]
  --debug      Switch loaders to debug mode                            [boolean]
  --devtool    A developer tool to enhance debugging.                   [string]
  -d           shortcut for --debug --devtool eval-cheap-module-source-map
               --output-pathinfo                                       [boolean]
  -p           shortcut for --optimize-minimize --define
               process.env.NODE_ENV="production"                       [boolean]
  --progress   Print compilation progress in percentage                [boolean]

Module options:
  --module-bind       Bind an extension to a loader                     [string]
  --module-bind-post  Bind an extension to a post loader                [string]
  --module-bind-pre   Bind an extension to a pre loader                 [string]

Output options:
  --output, -o                  The output path and file for compilation assets
  --output-path                 The output directory as **absolute path**
                                (required).
                                       [string] [default: The current directory]
  --output-filename             Specifies the name of each output file on disk.
                                You must **not** specify an absolute path here!
                                The `output.path` option determines the location
                                on disk the files are written to, filename is
                                used solely for naming the individual files.
                                                   [string] [default: [name].js]
  --output-chunk-filename       The filename of non-entry chunks as relative
                                path inside the `output.path` directory.
       [string] [default: filename with [id] instead of [name] or [id] prefixed]
  --output-source-map-filename  The filename of the SourceMaps for the
                                JavaScript files. They are inside the
                                `output.path` directory.                [string]
  --output-public-path          The `publicPath` specifies the public URL
                                address of the output files when referenced in a
                                browser.                                [string]
  --output-jsonp-function       The JSONP function used by webpack for async
                                loading of chunks.                      [string]
  --output-pathinfo             Include comments with information about the
                                modules.                               [boolean]
  --output-library              Expose the exports of the entry point as library
                                                                         [array]
  --output-library-target       Type of library
         [string] [choices: "var", "assign", "this", "window", "self", "global",
      "commonjs", "commonjs2", "commonjs-module", "amd", "umd", "umd2", "jsonp"]

Advanced options:
  --records-input-path       Store compiler state to a json file.       [string]
  --records-output-path      Load compiler state from a json file.      [string]
  --records-path             Store/Load compiler state from/to a json file. This
                             will result in persistent ids of modules and
                             chunks. An absolute path is expected. `recordsPath`
                             is used for `recordsInputPath` and
                             `recordsOutputPath` if they left undefined.[string]
  --define                   Define any free var in the bundle          [string]
  --target                   Environment to build for                   [string]
  --cache                    Cache generated modules and chunks to improve
                             performance for multiple incremental builds.
                      [boolean] [default: It's enabled by default when watching]
  --watch-stdin, --stdin     Stop watching when stdin stream has ended [boolean]
  --watch-aggregate-timeout  Delay the rebuilt after the first change. Value is
                             a time in ms.                              [number]
  --watch-poll               Enable polling mode for watching           [string]
  --hot                      Enables Hot Module Replacement            [boolean]
  --prefetch                 Prefetch this request (Example: --prefetch
                             ./file.js)                                 [string]
  --provide                  Provide these modules as free vars in all modules
                             (Example: --provide jQuery=jquery)         [string]
  --labeled-modules          Enables labeled modules                   [boolean]
  --plugin                   Load this plugin                           [string]
  --bail                     Report the first error as a hard error instead of
                             tolerating it.            [boolean] [default: null]
  --profile                  Capture timing information for each module.
                                                       [boolean] [default: null]

Resolving options:
  --resolve-alias         Redirect module requests                      [string]
  --resolve-extensions    Redirect module requests                       [array]
  --resolve-loader-alias  Setup a loader alias for resolving            [string]

Optimizing options:
  --optimize-max-chunks      Try to keep the chunk count below a limit
  --optimize-min-chunk-size  Minimal size for the created chunk
  --optimize-minimize        Enable minimizing the output. Uses
                             optimization.minimizer.                   [boolean]

Stats options:
  --color, --colors               Force colors on the console
                                           [boolean] [default: (supports-color)]
  --no-color, --no-colors         Force no colors on the console       [boolean]
  --sort-modules-by               Sorts the modules list by property in module
                                                                        [string]
  --sort-chunks-by                Sorts the chunks list by property in chunk
                                                                        [string]
  --sort-assets-by                Sorts the assets list by property in asset
                                                                        [string]
  --hide-modules                  Hides info about modules             [boolean]
  --display-exclude               Exclude modules in the output         [string]
  --display-modules               Display even excluded modules in the output
                                                                       [boolean]
  --display-max-modules           Sets the maximum number of visible modules in
                                  output                                [number]
  --display-chunks                Display chunks in the output         [boolean]
  --display-entrypoints           Display entry points in the output   [boolean]
  --display-origins               Display origins of chunks in the output
                                                                       [boolean]
  --display-cached                Display also cached modules in the output
                                                                       [boolean]
  --display-cached-assets         Display also cached assets in the output
                                                                       [boolean]
  --display-reasons               Display reasons about module inclusion in the
                                  output                               [boolean]
  --display-depth                 Display distance from entry point for each
                                  module                               [boolean]
  --display-used-exports          Display information about used exports in
                                  modules (Tree Shaking)               [boolean]
  --display-provided-exports      Display information about exports provided
                                  from modules                         [boolean]
  --display-optimization-bailout  Display information about why optimization
                                  bailed out for modules               [boolean]
  --display-error-details         Display details about errors         [boolean]
  --display                       Select display preset
              [string] [choices: "", "verbose", "detailed", "normal", "minimal",
                                                          "errors-only", "none"]
  --verbose                       Show more details                    [boolean]
  --info-verbosity                Controls the output of lifecycle messaging
                                  e.g. Started watching files...
                 [string] [choices: "none", "info", "verbose"] [default: "info"]
  --build-delimiter               Display custom text after build output[string]

Options:
  --help, -h     Show help                                             [boolean]
  --version, -v  Show version number                                   [boolean]
  --silent       Prevent output from being displayed in stdout         [boolean]
  --json, -j     Prints the result as JSON.

但是Java的是一个横杠

Usage: java [-options] class [args...]
           (to execute a class)
   or  java [-options] -jar jarfile [args...]
           (to execute a jar file)
where options include:
    -d32          use a 32-bit data model if available
    -d64          use a 64-bit data model if available
    -server       to select the "server" VM
    -zero         to select the "zero" VM
    -dcevm        to select the "dcevm" VM
                  The default VM is server,
                  because you are running on a server-class machine.


    -cp <class search path of directories and zip/jar files>
    -classpath <class search path of directories and zip/jar files>
                  A : separated list of directories, JAR archives,
                  and ZIP archives to search for class files.
    -D<name>=<value>
                  set a system property
    -verbose:[class|gc|jni]
                  enable verbose output
    -version      print product version and exit
    -version:<value>
                  Warning: this feature is deprecated and will be removed
                  in a future release.
                  require the specified version to run
    -showversion  print product version and continue
    -jre-restrict-search | -no-jre-restrict-search
                  Warning: this feature is deprecated and will be removed
                  in a future release.
                  include/exclude user private JREs in the version search
    -? -help      print this help message
    -X            print help on non-standard options
    -ea[:<packagename>...|:<classname>]
    -enableassertions[:<packagename>...|:<classname>]
                  enable assertions with specified granularity
    -da[:<packagename>...|:<classname>]
    -disableassertions[:<packagename>...|:<classname>]
                  disable assertions with specified granularity
    -esa | -enablesystemassertions
                  enable system assertions
    -dsa | -disablesystemassertions
                  disable system assertions
    -agentlib:<libname>[=<options>]
                  load native agent library <libname>, e.g. -agentlib:hprof
                  see also, -agentlib:jdwp=help and -agentlib:hprof=help
    -agentpath:<pathname>[=<options>]
                  load native agent library by full pathname
    -javaagent:<jarpath>[=<options>]
                  load Java programming language agent, see java.lang.instrument
    -splash:<imagepath>
                  show splash screen with specified image
See http://www.oracle.com/technetwork/java/javase/documentation/index.html for more details.