并行运行脚本命令

Question

i've bash script which I need to run on it two command in parallel

For example I'm executing a command of npm install which takes some time (20 -50 secs)

and I run it on two different folders in sequence first npm install on books folder and the second is for orders folder, is there a way to run both in parallel in shell script ?

For example assume the script is like following:

#!/usr/bin/env bash

   dir=$(pwd)

  cd $tmpDir/books/  

  npm install

  grunt

  npm prune production 
  cd $tmpDir/orders/

  npm install

  grunt

 npm prune production 

Answer 1

You could use & to run the process in the background, for example:

#!/bin/sh

cd $HOME/project/books/
npm install &

cd $HOME/project/orders/
npm install &

# if want to wait for the processes to finish
wait

To run and wait for nested/multiple processes you could use a subshell () for example:

#!/bin/sh

(sleep 10 && echo 10 && sleep 1 && echo 1) &

cd $HOME/project/books/
(npm install && grunt && npm prune production ) &

cd $HOME/project/orders/
(npm install && grunt && npm prune production ) &

# waiting ...
wait

In this case, notice the that the commands are within () and using && that means that only the right side will be evaluated if the left size succeeds (exit 0) so for the example:

(sleep 10 && echo 10 && sleep 1 && echo 1) &

• It creates a subshell putting things between ()
• runs sleep 10 and if succeeds && then runs echo 10 , if succeeds && then run sleep 1 and if succeeds && then runs echo 1
• run all this in the background by ending the command with &