How to run a shell script when a file or directory changes?

You may try entr tool to run arbitrary commands when files change. Example for files:

$ ls -d * | entr sh -c 'make && make test'

or:

$ ls *.css *.html | entr reload-browser Firefox

or print Changed! when file file.txt is saved:

$ echo file.txt | entr echo Changed!

For directories use -d, but you've to use it in the loop, e.g.:

while true; do find path/ | entr -d echo Changed; done

or:

while true; do ls path/* | entr -pd echo Changed; done

I use this script to run a build script on changes in a directory tree:

#!/bin/bash -eu
DIRECTORY_TO_OBSERVE="js"      # might want to change this
function block_for_change {
  inotifywait --recursive \
    --event modify,move,create,delete \
    $DIRECTORY_TO_OBSERVE
}
BUILD_SCRIPT=build.sh          # might want to change this too
function build {
  bash $BUILD_SCRIPT
}
build
while block_for_change; do
  build
done

Uses inotify-tools. Check inotifywait man page for how to customize what triggers the build.

Use inotify-tools.

The linked Github page has a number of examples; here is one of them.

#!/bin/sh

cwd=$(pwd)

inotifywait -mr \
  --timefmt '%d/%m/%y %H:%M' --format '%T %w %f' \
  -e close_write /tmp/test |
while read -r date time dir file; do
       changed_abs=${dir}${file}
       changed_rel=${changed_abs#"$cwd"/}

       rsync --progress --relative -vrae 'ssh -p 22' "$changed_rel" \
           [email protected]:/backup/root/dir && \
       echo "At ${time} on ${date}, file $changed_abs was backed up via rsync" >&2
done

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

Check out the kernel filesystem monitor daemon

http://freshmeat.net/projects/kfsmd/

Here's a how-to:

http://www.linux.com/archive/feature/124903