Preview #

To make myself to distinguish the spawn fork exec etc subprocess command, I need to look through the official docs to make a record.

pipe #

when we spawn a subprocess, there’s a pipe to connect the main process and the subprocess, called pipe. But the pipe has some limits like output limit, so if the subprocess writes to stdout in excess of limit, the subprocess will be blocked and wait for the pipe buffer for more data. use {stdio: 'ignore'} if the output will not be consumed.

command lookup #

if you specify the options.env.PATH, then the command lookup w/ this, otherwise will use the ({}).PATH

potential issue on Windows #

Node.js sorts the env lexicographically, but Windows is case-insensitive, so be careful when you pass multiple variants of the same key, such as PATH and Path, that’s to say, is you pass {path: xxx, PATH:xxx}, path will be consumed.

related api #

child_process module provides a handfule of sync and async alternatives to spawn and spawnSync

let’s see the differences

• spawn: spawn child process asyncly w/o blocking the Node.js event loop
• exec: spawn a shell and run command in that shell
• execFile: spawn the command directly w/o first spawning a shell by default
• fork spawn a new Node.js process and invokes a specified module w/ an IPC communication channel established that alows sending msg between parent and child.

the importance of the distinction between exec and the execFile can vary based on platform. On Unix-type platform, execFile is more efficient one since it not creates shell. On Windows, however, .bat and .cmd files are not executeable on their own w/o a terminal, so we have to use exec here.

and if the file name contains spaces, it needs to quoted:

 exec('"my script.cmd"')

spawn child process #

this means each process has its own memory, w/ their own V8 instancs.

shell #

Shell is a command-line interpreter that allows the user to interact with the system. It is responsible for taking inputs from the user and displaying the output.

A shell script needs to be saved with the extension .sh.

To let the Linux system know that the file is a shell script, the file needs to begin with the shebang construct.

shebang #

this #! is called shebang or hashbang, it’s used to specify the interpreter

#!/bin/bash 
OR
#!/bin/sh

executable file #

• appearance: no file extension and system can process it