Methods and examples of calling system commands, Shell scripts and Python scripts in Nodejs_node.js

Each language has its own advantages. When combined with each other, the program will execute more efficiently or whichever implementation method is simpler. Nodejs uses child processes to call system commands or files and documents. See http://nodejs.org/api/child_process.html. NodeJS child process provides important interfaces for interacting with the system. Its main APIs are: interfaces for standard input, standard output and standard error output.

NodeJS child process provides an important interface for interacting with the system. Its main APIs are:

Interfaces for standard input, standard output and standard error output

child.stdin gets standard input
child.stdout gets standard output
child.stderr gets standard error output
Get the PID of the child process: child.pid
Provides a method to generate a child process: child_process.spawn(cmd, args=[], [options])
Provides a method to directly execute system commands: child_process.exec(cmd, [options], callback)
Provides a method for calling script files: child_process.execFile(file, [args], [options], [callback])
Provides a method to kill the process: child.kill(signal='SIGTERM')

Let’s use an example to feel it, it’s very interesting, haha~~

1. Use child processes to call system commands (obtain system memory usage)

Create a new nodejs file named cmd_spawn.js with the following code:

Copy code The code is as follows:

var spawn = require('child_process').spawn;
free = spawn('free', ['-m']);

// Capture standard output and print it to the console
free.stdout.on('data', function (data) {
console.log('standard output:n' data);
});

// Capture standard error output and print it to the console
free.stderr.on('data', function (data) {
console.log('standard error output:n' data);
});

//Register child process shutdown event
free.on('exit', function (code, signal) {
console.log('child process eixt ,exit:' code);
});

The following are the results of running this script and running the command 'free -m' directly, which are exactly the same:

2. Execute system command (child_process.exec())

I still use this one very often, and its functions feel a little more powerful than the ones above. For example, I like to pay attention to the weather. Now I want to curl the weather interface to return data in json format. Maybe I need to perform some operations on it, so I will print it out and not operate it.

Create a new nodejs file named cmd_exec.js:

Copy code The code is as follows:

var exec = require('child_process').exec;
var cmdStr = 'curl http://www.weather.com.cn/data/sk/101010100.html';
exec(cmdStr, function(err,stdout,stderr){
If(err) {
console.log('get weather api error:' stderr);
} else {
          /*
The content of this stdout is what I curled out above:
{"weatherinfo":{"city":"Beijing","cityid":"101010100","temp":"3","WD":"Northwest Wind","WS":"Level 3","SD ":"23%","WSE":"3","time":"21:20","isRadar":"1","Radar":"JC_RADAR_AZ9010_JB","njd":"No live broadcast yet" ,"qy":"1019"}}
*/
        var data = JSON.parse(stdout);
console.log(data);
}
});

Let’s feel that the result of curling it directly and running the script are the same:

3. Call the shell script passing parameters (child_process.execFile())

This requires preparing a shell script first. For example, if I want to connect to a server to change its password, I need to provide the IP, user, new pwd, old pwd, and create a new shell script file change_password.sh:

Copy code The code is as follows:

#!/bin/sh

IP=""
NAME=""
PASSWORD=""
NEWPASSWORD=""

while getopts "H:U:P:N:" arg #The colon after the option indicates that the option requires parameters
do
case $arg in
H)
IP=$OPTARG
;;
U)
NAME=$OPTARG
;;
             P)
                   PASSWORD=$OPTARG
;;
                N)
                 NEWPASSWORD=$OPTARG
;;
                  ?)  #When there are options that are not recognized, the arg is?
                  echo "Contains unknown parameters"
exit 1
;;
      esac
done

#Get userid first
USERID=`/usr/bin/ipmitool -I lanplus -H $IP -U $NAME -P $PASSWORD user list | grep root | awk '{print $1}'`
# echo $USERID
#Change password based on userid
/usr/bin/ipmitool -I lanplus -H $IP -U $NAME -P $PASSWORD user set password $USERID $NEWPASSWORD

Then I prepare a nodejs file to call this shell script, called file_changepwd.js:

Copy code The code is as follows:

var callfile = require('child_process');
var ip = '1.1.1.1';
var username = 'test';
var password = 'pwd';
var newpassword = 'newpwd';

callfile.execFile('change_password.sh',['-H', ip, '-U', username, '-P', password, '-N', newpassword],null,function (err, stdout , stderr) {
​ callback(err, stdout, stderr);
});

It is not convenient to post the running results here, but I can personally guarantee that it has been tested.

After reading the above, there is actually no suspense about calling the python script. In essence, it is to execute the command.

4. Call the python script (the python script itself passes parameters)

Insert a digression here. The following paragraph is a brief explanation of parameters passed in python:

Copy code The code is as follows:

# -*-coding:utf-8 -*-
'''
Required module: sys
Number of parameters: len(sys.argv)
Script name: sys.argv[0]
Parameter 1: sys.argv[1]
Parameter 2: sys.argv[2]
'''
import sys
print u"script name:", sys.argv[0]
for i in range(1, len(sys.argv)): #The parameters here start from 1
Print u"parameter", i, sys.argv[i]

Run result:

I will also prepare a nodejs file to call this python script (I made modifications to py_test.py, see below), file_python.js:

Copy code The code is as follows:

var exec = require('child_process').exec;
var arg1 = 'hello'
var arg2 = 'jzhou'
exec('python py_test.py ' arg1 ' ' arg2 ' ',function(error,stdout,stderr){
If(stdout.length >1){
console.log('you offer args:',stdout);
} else {
console.log('you don't offer args');
}
If(error) {
console.info('stderr : ' stderr);
}
});

The content of py_test.py is as follows:
# -*-coding:utf-8 -*-
import sys
print sys.argv

The running results are as follows:

It’s still very good, and I have completed another exquisite blog for 2014. Haha~~