linux script that monitors file changes within folders (like autospec does!)

I want to automatically kick off a build whenever a file changes.

I've used autospec (RSpec)开发者_运维百科 in Ruby and loved that.

How can this be done in bash?

Take a look at incron and inotify-tools.

keywords are inotifywait & inotifywatch commands

After reading replies to other posts, I found a post (now gone), I created this script :-

#!/bin/bash

sha=0
previous_sha=0

update_sha()
{
    sha=`ls -lR . | sha1sum`
}

build () {
    ## Build/make commands here
    echo
    echo "--> Monitor: Monitoring filesystem... (Press enter to force a build/update)"
}

changed () {
    echo "--> Monitor: Files changed, Building..."
    build
    previous_sha=$sha
}

compare () {
    update_sha
    if [[ $sha != $previous_sha ]] ; then changed; fi
}

run () {
    while true; do

        compare

        read -s -t 1 && (
            echo "--> Monitor: Forced Update..."
            build
        )

    done
}

echo "--> Monitor: Init..."
echo "--> Monitor: Monitoring filesystem... (Press enter to force a build/update)"
run

How about this script? Uses the 'stat' command to get the access time of a file and runs a command whenever there is a change in the access time (whenever file is accessed).

#!/bin/bash
while true
do
   ATIME=`stat -c %Z /path/to/the/file.txt`
   if [[ "$ATIME" != "$LTIME" ]]
   then
       echo "RUN COMMNAD"
       LTIME=$ATIME
   fi
   sleep 5
done

If you've entr installed, then in shell you can use the following syntax:

while true; do find src/ | entr -d make build; done

See this example as an improvement upon on Ian Vaughan's answer:

#!/usr/bin/env bash
# script:  watch
# author:  Mike Smullin <mike@smullindesign.com>
# license: GPLv3
# description:
#   watches the given path for changes
#   and executes a given command when changes occur
# usage:
#   watch <path> <cmd...>
#

path=$1
shift
cmd=$*
sha=0
update_sha() {
  sha=`ls -lR --time-style=full-iso $path | sha1sum`
}
update_sha
previous_sha=$sha
build() {
  echo -en " building...\n\n"
  $cmd
  echo -en "\n--> resumed watching."
}
compare() {
  update_sha
  if [[ $sha != $previous_sha ]] ; then
    echo -n "change detected,"
    build
    previous_sha=$sha
  else
    echo -n .
  fi
}
trap build SIGINT
trap exit SIGQUIT

echo -e  "--> Press Ctrl+C to force build, Ctrl+\\ to exit."
echo -en "--> watching \"$path\"."
while true; do
  compare
  sleep 1
done