File watcher shell script - for use with front-end polling script

watch.sh

#!/bin/bash

##
## This script watches for changes in the specified directories and runs the build
## script when changes are detected.
##
## It writes a .modified_time file to the root of the project. This contains the
## timestamp of the last modification time.
##
## This is intended to be used with a front-end script that polls for changes
## and reloads, such as:
##
## https://gist.github.com/rosswintle/ae6e47d52e4e5b06dfe197543be4c5eb
##
## If you use this, be sure to add the following to your .gitignore file:
##
## .modified_time
##

# Directories to monitor (modify as needed)
directories=(
    "src"
)

modifiedFilename=".modified_time"

# Project-global modification time file - in the public directory for a browser to check
projectModifiedTimeFile="public/$modifiedFilename"

# Echo the current timestamp to the file if it doesn't exist
if [[ ! -f "$projectModifiedTimeFile" ]]; then
    echo "$(date +%s)" > "$projectModifiedTimeFile"
fi

# Function to check for file changes in a directory
check_for_changes() {
    local dir="$1"
    local last_mtime=""

    if [[ -f "${dir}/$modifiedFilename" ]]; then
        last_mtime=$(cat "${dir}/$modifiedFilename")
    else
        # Create the file if it doesn't exist
        touch "${dir}/$modifiedFilename"
    fi

    if [[ "$(uname)" == "Darwin" ]]; then
        # MacOS
        new_mtime=$(find "$dir" -type f -not -name "$modifiedFilename" -exec stat -f '%m' {} \; | sort -n | tail -1)
    else
        # Assume Linux
        new_mtime=$(find "$dir" -type f -not -name "$modifiedFilename" -exec stat -c '%Y' {} \; | sort -n | tail -1)
    fi

    if [[ "$new_mtime" != "$last_mtime" ]]; then
        # Files have changed, run the build script
        echo "Files changed in $dir, running build.sh"
        ./build.sh

        # Update last modification time
        echo "$new_mtime" > "${dir}/$modifiedFilename"
        # Also update the global modification time
        echo "$new_mtime" > "$projectModifiedTimeFile"
    fi
}

# Main loop
while true; do
    for dir in "${directories[@]}"; do
        check_for_changes "$dir"
    done

    sleep 1
done