Sending command line arguments to npm script

Question

The scripts portion of my package json currently looks like this    scripts          start    node   script js server         which means I can run npm start to start the server  So far so good   However  I would like to be able to run something like npm start 8080 and have the argument s  passed to script js  e g  npm start 8080    node   script js server 8080   Is this possible

User · Answer

npm run script target --  lt  argument   Basically this is the way of passing the command line arguments but it will work only in case of when script have only one command running like I am running a command i e  npm run start -- 4200   script            start     ng serve --port        This will run for passing command line parameters but what if we run more then one command together like npm run build c  workspace file    script            build     copy c  file  lt arg gt   amp  amp  ng build        but it will interpreter like this while running copy c  file   amp  amp  ng build c  work space file and we are expected something like this  copy c  file  c  work space file   amp  amp  ng build  Note  - so command line parameter only work ad expected in case of only one command in a script   I read some answers above in which some of them are writing that you can access the command line parameter using   symbol but this will not gonna work

User · Answer

I know there is an approved answer already  but I kinda like this JSON approach   npm start    PROJECT NAME STR   my amazing stuff    CRAZY ARR   0 7  hungry     MAGICAL NUMBER INT   42   THING BOO  true      Usually I have like 1 var I need  such as a project name  so I find this quick n  simple   Also I often have something like this in my package json   scripts          start    NODE ENV development node local js      And being greedy I want  all of it   NODE ENV and the CMD line arg stuff   You simply access these things like so in your file  in my case local js   console log process env NODE ENV  starter obj CRAZY ARR  starter obj PROJECT NAME STR  starter obj MAGICAL NUMBER INT  starter obj THING BOO     You just need to have this bit above it  I m running v10 16 0 btw   var starter obj   JSON parse JSON parse process env npm config argv  remain 0      Anyhoo  question already answered  Thought I d share  as I use this method a lot

User · Answer

You asked to be able to run something like npm start 8080   This is possible without needing to modify script js or configuration files as follows   For example  in your  scripts  JSON value  include--   start    node   script js server  PORT    And then from the command-line     PORT 8080 npm start   I have confirmed that this works using bash and npm 1 4 23   Note that this work-around does not require GitHub npm issue  3494 to be resolved

User · Answer

Use process argv in your code then just provide a trailing    to your scripts value entry   As an example try it with a simple script which just logs the provided arguments to standard out echoargs js   console log  arguments      process argv slice 2      package json    scripts          start    node echoargs js         Examples    gt  npm start 1 2 3 arguments  1 2 3   process argv 0  is the executable  node   process argv 1  is your script   Tested with npm v5 3 0 and node v8 4 0

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If you want to pass arguments to the middle of an npm script  as opposed to just having them appended to the end  then inline environment variables seem to work nicely    scripts        dev    BABEL ARGS -w npm run build  amp  amp  cd lib server  amp  amp  nodemon index js      start    npm run build  amp  amp  node lib server index js      build    mkdir -p lib  amp  amp  babel  BABEL ARGS -s inline --stage 0 src -d lib        Here  npm run dev passes the -w watch flag to babel  but npm run start just runs a regular build once

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jakub g s answer is correct  however an example using grunt seems a bit complex   So my simpler answer   - Sending a command line argument to an npm script  Syntax for sending command line arguments to an npm script   npm run  command   --  lt args gt     Imagine we have an npm start task in our package json to kick off webpack dev server    scripts        start    webpack-dev-server --port 5000       We run this from the command line with npm start   Now if we want to pass in a port to the npm script    scripts        start    webpack-dev-server --port process env port    8080       running this and passing the port e g  5000 via command line would be as follows   npm start --port 5000   - Using package json config   As mentioned by jakub g  you can alternatively set params in the config of your package json   config        myPort    5000      scripts        start    webpack-dev-server --port process env npm package config myPort    8080       npm start will use the port specified in your config  or alternatively you can override it  npm config set myPackage myPort 3000   - Setting a param in your npm script  An example of reading a variable set in your npm script  In this example NODE ENV   scripts        start prod    NODE ENV prod node server js      start dev    NODE ENV dev node server js       read NODE ENV in server js either prod or dev  var env   process env NODE ENV     prod   if env      dev        var app   require    serverDev js      else       var app   require    serverProd js

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For PowerShell users on Windows The accepted answer did not work for me with npm 6 14  Neither adding no -- nor including it once does work  However  putting -- twice or putting  quot -- quot  once before the arguments does the trick  Example  npm run  lt my script gt  -- --  lt my arguments like --this gt   Suspected reason Like in bash  -- instructs PowerShell to treat all following arguments as literal strings  and not options  E g see this answer   The issues seems to be that the command is interpreted one time more than expected  loosing the  --   For instance  by doing npm run  lt my script gt  -- --option value  npm will run  lt my script gt  value  However  doing npm run  lt my script gt   quot -- quot  --option value  results in  lt my script gt   quot --option quot   quot value quot   which works fine

User · Answer

As of npm 2 x  you can pass args into run-scripts by separating with -- Terminal npm run-script start -- --foo 3  Package json  quot start quot    quot node   index js quot   Index js console log  process argv   process argv

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Note  This approach modifies your package json on the fly  use it if you have no alternative   I had to pass command line arguments to my scripts which were something like    scripts          start    npm run build  amp  amp  npm run watch        watch    concurrently    npm run watch-ts     npm run watch-node                 So  this means I start my app with npm run start   Now if I want to pass some arguments  I would start with maybe   npm run start -- --config someConfig   What this does is  npm run build  amp  amp  npm run watch -- --config someConfig  Problem with this is  it always appends the arguments to the end of the script  This means all the chained scripts don t get these arguments Args maybe or may not be required by all  but that s a different story    Further when the linked scripts are called then those scripts won t get the passed arguments  i e  The watch script won t get the passed arguments   The production usage of my app is as an  exe  so passing the arguments in the exe works fine but if want to do this during development  it gets problamatic   I couldn t find any proper way to achieve this  so this is what I have tried   I have created a javascript file  start-script js at the parent level of the application  I have a  default package json  and instead of maintaining  package json   I maintain  default package json   The purpose of start-script json is to read default package json  extract the scripts and look for npm run scriptname then append the passed arguments to these scripts  After this  it will create a new package json and copy the data from default package json with modified scripts and then call npm run start   const fs   require  fs    const   spawn     require  child process        open default package json const defaultPackage   fs readFileSync    default package json    try       const packageOb   JSON parse defaultPackage          loop over the scripts present in this object  edit them with flags     if   scripts  in packageOb  amp  amp  process argv length  gt  2             const passedFlags     --   process argv slice 2  join                    assuming the script names have words    or -  modify the regex if required          const regexPattern     npm run   w -    g          const scriptsWithFlags   Object entries packageOb scripts  reduce  acc   key  value     gt                const patternMatches   value match regexPattern                  loop over all the matched strings and attach the desired flags              if  patternMatches                    for  let eachMatchedPattern of patternMatches                        const startIndex   value indexOf eachMatchedPattern                       const endIndex   startIndex   eachMatchedPattern length                         save the string which doen t fall in this matched pattern range                      value   value slice 0  startIndex    eachMatchedPattern   passedFlags   value slice endIndex                                               acc key    value              return acc                          packageOb scripts   scriptsWithFlags             const modifiedJSON   JSON stringify packageOb  null  4       fs writeFileSync    package json   modifiedJSON           now run your npm start script     let cmd    npm          check if this works in your OS     if  process platform      win32             cmd    npm cmd         https   github com nodejs node issues 3675           spawn cmd    run    start      stdio   inherit         catch e        console log  Error while parsing default package json   e       Now  instead of doing npm run start  I do node start-script js --c somethis --r somethingElse   The initial run looks fine  but haven t tested thoroughly  Use it  if you like for you app development

User · Answer

npm 2 and newer It s possible to pass args to npm run since npm 2  2014   The syntax is as follows  npm run  lt command gt   --  lt args gt   Note the -- separator  used to separate the params passed to npm command itself  and the params passed to your script  With the example package json     quot scripts quot          quot grunt quot    quot grunt quot        quot server quot    quot node server js quot       here s how to pass the params to those scripts  npm run grunt -- task target     invokes  grunt task target  npm run server -- --port 1337    invokes  node server js --port 1337   Note  If your param does not start with - or --  then having an explicit -- separator is not needed  but it s better to do it anyway for clarity  npm run grunt task target        invokes  grunt task target   Note below the difference in behavior  test js has console log process argv    the params which start with - or -- are passed to npm and not to the script  and are silently swallowed there    npm run test foobar   C   Program Files  nodejs  node exe    C   git  myrepo  test js     foobar      npm run test -foobar   C   Program Files  nodejs  node exe    C   git  myrepo  test js      npm run test --foobar   C   Program Files  nodejs  node exe    C   git  myrepo  test js      npm run test -- foobar   C   Program Files  nodejs  node exe    C   git  myrepo  test js    foobar      npm run test -- -foobar   C   Program Files  nodejs  node exe    C   git  myrepo  test js    -foobar      npm run test -- --foobar   C   Program Files  nodejs  node exe    C   git  myrepo  test js    --foobar    The difference is clearer when you use a param actually used by npm    npm test --help         this is disguised  npm --help test  npm test  --  lt args gt    aliases  tst  t  To get the parameter value  see this question  For reading named parameters  it s probably best to use a parsing library like yargs or minimist  nodejs exposes process argv globally  containing command line parameter values  but this is a low-level API  whitespace-separated array of strings  as provided by the operating system to the node executable    Edit 2013 10 03  It s not currently possible directly  But there s a related GitHub issue opened on npm to implement the behavior you re asking for  Seems the consensus is to have this implemented  but it depends on another issue being solved before   Original answer  2013 01   As a some kind of workaround  though not very handy   you can do as follows  Say your package name from package json is myPackage and you have also  quot scripts quot          quot start quot    quot node   script js server quot     Then add in package json   quot config quot          quot myPort quot    quot 8080 quot     And in your script js     defaulting to 8080 in case if script invoked not via  quot npm run-script quot  but directly var port   process env npm package config myPort    8080  That way  by default npm start will use 8080  You can however configure it  the value will be stored by npm in its internal storage   npm config set myPackage myPort 9090  Then  when invoking npm start  9090 will be used  the default from package json gets overridden

User · Answer

Most of the answers above cover just passing the arguments into your NodeJS script  called by npm  My solution is for general use   Just wrap the npm script with a shell interpreter  e g  sh  call and pass the arguments as usual  The only exception is that the first argument number is 0   For example  you want to add the npm script someprogram --env  lt argument 1 gt   where someprogram just prints the value of the env argument   package json   scripts        command    sh -c  someprogram --env  0       When you run it     npm run -s command my-environment my-environment

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I ve found this question while I was trying to solve my issue with running sequelize seed generate cli command   node modules  bin sequelize seed generate --name user   Let me get to the point  I wanted to have a short script command in my package json file and to provide --name argument at the same time  The answer came after some experiments  Here is my command in package json   scripts       seed generate   NODE ENV development node modules  bin sequelize seed generate          and here is an example of running it in terminal to generate a seed file for a user   gt  yarn seed generate --name user   gt  npm run seed generate -- --name user   FYI  yarn -v 1 6 0  npm -v 5 6 0

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From what I see  people use package json scripts when they would like to run script in simpler way  For example  to use nodemon that installed in local node modules  we can t call nodemon directly from the cli  but we can call it by using   node modules nodemon nodemon js  So  to simplify this long typing  we can put this                    scripts           start    nodemon app js                        then call npm start to use  nodemon  which has app js as the first argument   What I m trying to say  if you just want to start your server with the node command  I don t think you need to use scripts  Typing npm start or node app js has the same effort   But if you do want to use nodemon  and want to pass a dynamic argument  don t use script either  Try to use symlink instead   For example using migration with sequelize  I create a symlink     ln -s node modules sequelize bin sequelize sequelize      And I can pass any arguement when I call it        sequlize -h    show help       sequelize -m    upgrade migration       sequelize -m -u    downgrade migration      etc     At this point  using symlink is the best way I could figure out  but I don t really think it s the best practice   I also hope for your opinion to my answer

User · Answer

This doesn t really answer your question but you could always use environment variables instead    scripts          start    PORT 3000 node server js      Then in your server js file   var port   process env PORT    3000

User · Answer

You could also do that   In package json    scripts          cool      cool js      In cool js    console log   myVar  process env npm config myVar       In CLI   npm --myVar something run-script cool   Should output     myVar   something      Update  Using npm 3 10 3  it appears that it lowercases the process env npm config  variables  I m also using better-npm-run  so I m not sure if this is vanilla default behavior or not  but this answer is working  Instead of process env npm config myVar  try process env npm config myvar

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I had been using this one-liner in the past  and after a bit of time away from Node js had to try and rediscover it recently  Similar to the solution mentioned by  francoisrv  it utilizes the node config   variables   Create the following minimal package json file        name    argument      version    1 0 0      scripts          argument    echo   The value of --foo is    npm config foo              Run the following command   npm run argument --foo bar   Observe the following output      The value of --foo is  bar    All of this is nicely documented in the npm official documentation    https   docs npmjs com using-npm config   Note  The Environment Variables heading explains that variables inside scripts do behave differently to what is defined in the documentation  This is true when it comes to case sensitivity  as well whether the argument is defined with a space or equals sign   Note  If you are using an argument with hyphens  these will be replaced with underscores in the corresponding environment variable  For example  npm run example --foo-bar baz would correspond to   npm config foo bar    Note  For non-WSL Windows users  see  Doctor Blue s comments below    TL DR replace   npm config foo  with  npm config foo

User · Answer

I find it s possible to just pass variables exactly as you would to Node js     index js console log process env TEST ENV VAR      package json      quot scripts quot      quot start quot    quot node index js quot          TEST ENV VAR hello npm start  Prints out  quot hello quot

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