Bash script, watch folder, execute command

Question

I am trying to create a bash script with 2 parameters:

• a directory
• a command.

I want to watch the directory parameter for changes: when something has been changed the script should execute the command.

I'm running MacOS, not Linux; any pointers or external resources would greatly help as I have see that this is difficult to achieve. Really OI am trying to mimic SASS's watch functionality.

#!/bin/bash

#./watch.sh $PATH $COMMAND

DIR=$1  

ls -l $DIR > $DIR/.begin
#this does not work
DIFFERENCE=$(diff .begin .end)

if [ $DIFFERENCE = '\n']; then
    #files are same
else
    $2
fi 

ls -l $DIR > $DIR/.end

Answer 1

Here's an example of watching a folder for changes and running a the less compiler when one is updated. As a prereq you need npm and these the module onchange. The node community has a whole bunch of different watch commands (like onchange) I'm not aware of any that are compiled self-contained binaries.

npm install less onchange -g

Then you can use something like:

onchange "./stylesheets/*.less" -- lessc main.less > main.css

I prefer a BASH command over the Grunt answer I gave a while back.