node js shell command execution

Question

I am still trying to grasp the finer points of how I can run a linux or windows shell command and capture output within node js  ultimately  I want to do something like this       pseudocode output   run command cmd  args    The important piece is that output must be available to a globally scoped variable  or object    I tried the following function  but for some reason  I get undefined printed to the console     function run cmd cmd  args  cb      var spawn   require  child process   spawn   var child   spawn cmd  args     var me   this    child stdout on  data   function me  data        cb me  data           foo   new run cmd  dir      B    function  me  data  me stdout data     console log foo stdout       yields  undefined   lt ------   I m having trouble understanding where the code breaks above    a very simple prototype of that model works     function try this cmd  cb      var me   this    cb me  cmd    bar   new try this  guacamole   function  me  cmd  me output cmd    console log bar output      yields  guacamole   lt ----   Can someone help me understand why try this   works  and run cmd   does not   FWIW  I need to use child process spawn  because child process exec has a 200KB buffer limit   Final Resolution  I m accepting James White s answer  but this is the exact code that worked for me     function cmd exec cmd  args  cb stdout  cb end      var spawn   require  child process   spawn      child   spawn cmd  args       me   this    me exit   0      Send a cb to set 1 when cmd exits   me stdout         child stdout on  data   function  data    cb stdout me  data        child stdout on  end   function      cb end me        foo   new cmd exec  netstat     -rn       function  me  data   me stdout    data toString        function  me   me exit   1      function log console       console log foo stdout     setTimeout       wait 0 25 seconds and print the output   log console  250

User · Answer

You re not actually returning anything from your run cmd function   function run cmd cmd  args  done        var spawn   require  child process   spawn      var child   spawn cmd  args       var result     stdout            child stdout on  data   function  data                result stdout    data              child stdout on  end   function                  done                return result      gt  foo   run cmd  ls     -al    function      console log  done           stdout       done   gt  foo stdout  total 28520       Works just fine

User · Answer

A simplified version of the accepted answer  third point   just worked for me   function run cmd cmd  args  callBack         var spawn   require  child process   spawn      var child   spawn cmd  args       var resp            child stdout on  data   function  buffer    resp    buffer toString           child stdout on  end   function     callBack  resp                Usage   run cmd   ls     -l    function text    console log  text       run cmd   hostname       function text    console log  text

User · Answer

TonyO Hagan is comprehrensive shelljs answer  but  I would like to highlight the synchronous version of his answer   var shell   require  shelljs    var output   shell exec  netstat -rn    silent true   output  console log output

User · Answer

I had a similar problem and I ended up writing a node extension for this  You can check out the git repository  It s open source and free and all that good stuff    https   github com aponxi npm-execxi     ExecXI is a node extension written in C   to execute shell commands   one by one  outputting the command s output to the console in   real-time  Optional chained  and unchained ways are present  meaning   that you can choose to stop the script after a command fails    chained   or you can continue as if nothing has happened     Usage instructions are in the ReadMe file  Feel free to make pull requests or submit issues   I thought it was worth to mention it

User · Answer

Synchronous one-liner  require  child process   execSync  quot echo  hi  quot   function puts error  stdout  stderr    console log stdout

User · Answer

There are three issues here that need to be fixed   First is that you are expecting synchronous behavior while using stdout asynchronously  All of the calls in your run cmd function are asynchronous  so it will spawn the child process and return immediately regardless of whether some  all  or none of the data has been read off of stdout  As such  when you run  console log foo stdout     you get whatever happens to be stored in foo stdout at the moment  and there s no guarantee what that will be because your child process might still be running   Second is that stdout is a readable stream  so 1  the data event can be called multiple times  and 2  the callback is given a buffer  not a string  Easy to remedy  just change  foo   new run cmd       netstat exe     -an    function  me  data  me stdout data        into  foo   new run cmd       netstat exe     -an    function  me  buffer  me stdout  buffer toString          so that we convert our buffer into a string and append that string to our stdout variable   Third is that you can only know you ve received all output when you get the  end  event  which means we need another listener and callback   function run cmd cmd  args  cb  end                   child stdout on  end   end       So  your final result is this   function run cmd cmd  args  cb  end        var spawn   require  child process   spawn          child   spawn cmd  args           me   this      child stdout on  data   function  buffer    cb me  buffer          child stdout on  end   end         Run C  Windows System32 netstat exe -an var foo   new run cmd       netstat exe     -an        function  me  buffer    me stdout    buffer toString          function      console log foo stdout

User · Answer

A promisified version of the most-awarded answer     runCmd   cmd  args    gt        return new Promise  resolve  reject    gt          var spawn   require  child process   spawn       var child   spawn cmd  args        var resp            child stdout on  data   function  buffer    resp    buffer toString            child stdout on  end   function      resolve resp                  To use    runCmd  ls   then ret   gt  console log ret

User · Answer

Simplest way is to just use the ShellJS lib        npm install  -g  shelljs   EXEC Example   require  shelljs global        Sync call to exec   var version   exec  node --version    silent true   output      Async call to exec   exec  netstat exe -an   function status  output      console log  Exit status    status     console log  Program output    output         ShellJs org supports many common shell commands mapped as NodeJS functions including    cat cd chmod cp dirs echo exec exit find grep ln ls mkdir mv popd pushd pwd rm sed test which

User · Answer

I used this more concisely    var sys   require  sys   var exec   require  child process   exec  function puts error  stdout  stderr    sys puts stdout    exec  ls -la   puts     it works perfectly

User · Answer

There s a variable conflict in your run cmd function     var me   this    child stdout on  data   function me  data           me is overriden by function argument     cb me  data           Simply change it to this     var me   this    child stdout on  data   function data           One argument only      cb me  data           In order to see errors always add this     child stderr on  data   function data          console log  data            EDIT You re code fails because you are trying to run dir which is not provided as a separate standalone program  It is a command in cmd process  If you want to play with filesystem use native require   fs      Alternatively   which I do not recommend   you can create a batch file which you can then run  Note that OS by default fires batch files via cmd

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