Share the method of calling system commands using NodeJS's child process (child_process)

Share the method of calling system commands using NodeJS's child process (child_process)_json

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Release： 2016-05-16 17:32:43

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Introduction to NodeJS subprocess NodeJS subprocess provides important interfaces for interacting with the system. Its main APIs are: interfaces for standard input, standard output, and standard error output.

Introduction to NodeJS subprocess

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

Standard input, standard output and standard error output interface
child.stdin Get standard input
child.stdout Get standard output
child.stderr Get standard error output
Get the PID of the child process: child.pid
Provided Important methods for generating child processes: child_process.spawn(cmd, args=[], [options])
Provides important methods for directly executing system commands: child_process.exec(cmd, [options], callback)
Provided Method to kill the process: child.kill(signal='SIGTERM')

Example 1: Use the child process to obtain system memory usage

Save the following code as free.js:

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:
' data); 
}); 

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

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

Result after executing the code:

$ node free.js
Stdout :
total used free shared buffers cached
Mem: 3949 1974 1974 0 135 959
-/ buffers/cache: 879 3070
Swap: 3905 0 3905

The child process has exited , Code: 0
The above output is equivalent to executing the free -m command on the command line.

Through this simple example, we have already understood the use of child processes. Here is another example to demonstrate the use of exec.

Example 2: Using child processes to count system login times

Save the following code as last.js

Copy code The code is as follows:

 
var exec = require('child_process').exec, 
last = exec('last | wc -l'); 

last.stdout.on('data', function (data) { 
console.log('Stdout:' data); 
}); 
 
last.on('exit', function (code) { 
console.log('The child process has been closed, code: ' code); 
}); 

Execution code:

$ node last.js
Standard output: 203

The child process has been closed, code: 0
It is the same as typing directly on the command line: last | wc - The result for l is the same.