node. JS Notes (ix) Nodejs and Shell

As we all know, Nodejs is a single-process asynchronous operation, but not just a single process, Nodejs also provides multi-process support
Its founders should still pay more attention to this piece, the strongest evidence is that child_process is one of the NODEJS core modules

This module should not be used in most cases, but child_process can do a lot of interesting things.

Shell calls

Recently used more practical functions, in large data processing, the need to be based on the customer click on the page to convert to spark cluster command
Spark was written in Scala, and it didn't have anything to do with Nodejs.
After considering a period of time, decided to use the Shell to solve

Shell Script Basics
The shell is actually very simple, you lose a CD desktop in the console and then enter, this is the simplest shell command,
Writing this line of instructions in the text is the shell script.
For example:
test.sh

#!bin/bashspark-submit test.jar para1 para2......

Commands can be used under the *nix system

sh test.sh

To execute this script with the effect of a direct knock command

spark-submit test.jar para1 para2......

is the same.

the ExecFile method of Nodejs
The prototype is as follows:

child_process.execfile (file, args, options, callback) Description: File {string}  the file name of the program to run args {array}  string parameter list options {object}  cwd {string}  Sub-process current working directory env {object}  environment variable key value pair encoding {string}  Encoding (default =  ' UTF8 ' ) timeout {number}  timeout (default = 0 ) maxbuffer {number}  maximum buffering (default = 200  *1024 ) killsignal {string}  end signal (default =  ' SIGTERM ' ) callback {function}  process end callback with output error Span class= "Hljs-list" >{error}  stdout {buffer}  stderr {buffer}  return: Childprocess object 

The use is also very simple, it is worth noting that there are three points

1. Timeout
2. StdOut
3. StdErr

Using the shell to implement this cross-language invocation is often considered unstable,
Once the Linux EXEC command executes, the original process is replaced with a new process, which loses control of the new process.
For the first time, there was a shell error, for various reasons card death situation
Nodejs provides a better solution, and timeout solves the problem of card death
STDOUT and stderr provide standard output and error output so that the state of the child process can be obtained
Here's how to use it:

var  call_sh = require  ( ' child_process ' ); //para is an array of JSON format, which is obtained by post  function  callsh  Span class= "Hljs-params" > (File,para)  { call_sh.execfile (File,[para.attr1,para.attr2],function   (Error, stdout, stderr)     { console.log ( ' stdout: '  + stdout);    Console.log ( ' stderr: '  + stderr); if  (Error!== null )    {Console.log ( + error); }    });}

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node. JS Notes (ix) Nodejs and Shell