node js execute system command synchronously

Question

I need in node js function  result   execSync  node -v      that will synchronously execute the given command line and return all stdout ed by that command text      ps  Sync is wrong  I know  Just for personal use    UPDATE  Now we have mgutz s solution which gives us exit code  but not stdout  Still waiting for a more precise answer   UPDATE  mgutz updated his answer and the solution is here    Also  as dgo a mentioned  there is stand-alone module exec-sync  UPDATE 2014-07-30  ShellJS lib arrived  Consider this is the best choice for now     UPDATE 2015-02-10  AT LAST  NodeJS 0 12 supports execSync natively  See official docs

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I get used to implement  synchronous  stuff at the end of the callback function  Not very nice  but it works  If you need to implement a sequence of command line executions you need to wrap exec into some named function and recursively call it  This pattern seem to be usable for me   SeqOfExec someParam    function SeqOfExec somepParam           some stuff                                var execStr    yourExecString       child proc exec execStr  function  error  stdout  stderr            if  error    null                if  stdout                    throw Error  Smth goes wrong    error                 else                      consider that empty stdout causes                    creation of error object                                    some stuff                                               you also need some flag which will signal that you             need to end loop         if  someFlag                    your synch stuff after all execs                here                                else               SeqOfExec someAnotherParam

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you can do synchronous shell operations in nodejs like so   var execSync   function cmd         var exec    require  child process   exec      var fs   require  fs           for linux use   instead of  amp  amp        execute your command followed by a simple echo        to file to indicate process is finished     exec cmd      gt  c   stdout txt  amp  amp  echo done  gt  c   sync txt         while  true              consider a timeout option to prevent infinite loop           NOTE  this will max out your cpu too          try               var status   fs readFileSync  c   sync txt    utf8                 if  status trim       done                     var res   fs readFileSync  c   stdout txt    utf8                    fs unlinkSync  c   stdout txt      cleanup temp files                 fs unlinkSync  c   sync txt                    return res                          catch e        readFileSync will fail until file exists              won t return anything  but will take 10 seconds to run console log execSync  sleep 10         assuming there are a lot of files and subdirectories     this too may take a while  use your own applicable file path console log execSync  dir  s c   usr  docs         EDIT - this example is meant for windows environments  adjust for your own linux needs if necessary

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This is the easiest way I found      exec-Sync     https   github com jeremyfa node-exec-sync      Not to be confused with execSync        Execute shell command synchronously  Use this for migration scripts  cli programs  but not for regular server code       Example    var execSync   require  exec-sync       var user   execSync  echo  USER    console log user

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Native Node js solution is  const  execSync    require  child process     const result   execSync  node -v        this do the trick   Just be aware that some commands returns Buffer instead of string  And if you need string just add encoding to execSync options  const result   execSync  git rev-parse HEAD    encoding   utf8          and it is also good to have timeout on sync exec  const result   execSync  git rev-parse HEAD    encoding   utf8   timeout  10000

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I actually had a situation where I needed to run multiple commands one after another from a package json preinstall script in a way that would work on both Windows and Linux OSX  so I couldn t rely on a non-core module   So this is what I came up with    cmds coffee childproc   require  child process   exports exec    cmds  - gt    next   - gt      if cmds length  gt  0       cmd   cmds shift         console log  Running command    cmd         childproc exec cmd   err  stdout  stderr  - gt          if err  then console log err         if stdout  then console log stdout         if stderr  then console log stderr         next       else       console log  Done executing commands      console log  Running the follows commands     console log cmds   next     You can use it like this   require    cmds   exec   grunt coffee    nodeunit test tls-config js     EDIT  as pointed out  this doesn t actually return the output or allow you to use the result of the commands in a Node program   One other idea for that is to use LiveScript backcalls   http   livescript net

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Node js  since version 0 12 - so for a while  supports execSync   child process execSync command   options     You can now directly do this   const execSync   require  child process   execSync  code   execSync  node -v      and it ll do what you expect   Defaults to pipe the i o results to the parent process   Note that you can also spawnSync now

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You can achieve this using fibers  For example  using my Common Node library  the code would look like this   result   require  subprocess   command  node -v

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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   EDIT  However it doesn t return the stdout yet    Just outputs them in real-time  It does now  Well  I just released it today  Maybe we can build on it    Anyway  I thought it was worth to mention it

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Just to add that even though there are few usecases where you should use them  spawnSync   execFileSync   execSync were added to node js in these commits  https   github com joyent node compare d58c206862dc   e8df2676748e

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See execSync library   It s fairly easy to do with node-ffi  I wouldn t recommend for server processes  but for general development utilities it gets things done  Install the library   npm install node-ffi   Example script   var FFI   require  node-ffi    var libc   new FFI Library null       system     int32     string         var run   libc system  run  echo  USER       EDIT Jun 2012  How to get STDOUT   var lib   ffi Library null           FILE  popen char  cmd  char  mode       popen    pointer     string    string             void pclose FILE  fp       pclose    void      pointer             char  fgets char  buff  int buff  in      fgets    string     string    int   pointer         function execSync cmd      var     buffer   new Buffer 1024       result           fp   lib popen cmd   r       if   fp  throw new Error  execSync error    cmd      while lib fgets buffer  1024  fp         result    buffer readCString           lib pclose fp      return result     console log execSync  echo  HOME

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There s an excellent module for flow control in node js called asyncblock  If wrapping the code in a function is OK for your case  the following sample may be considered   var asyncblock   require  asyncblock    var exec   require  child process   exec   asyncblock function  flow        exec  node -v   flow add         result   flow wait        console log result         There ll be trailing  n in the output         Some other jobs     console log  More results like if it were sync

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This is not possible in Node js  both child process spawn and child process exec were built from the ground up to be async   For details see  https   github com ry node blob master lib child process js  If you really want to have this blocking  then put everything that needs to happen afterwards in a callback  or build your own queue to handle this in a blocking fashion  I suppose you could use Async js for this task   Or  in case you have way too much time to spend  hack around in Node js it self

User · Answer

Use ShellJS module   exec function without providing callback   Example   var version   exec  node -v   output

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