Mdthbs

If you have inotify-tools installed (at least that's the package name on Debian) when you can do something like this:

while inotifywait -q -e modify filename >/dev/null; do

    echo "filename is changed"

    # do whatever else you need to do

done

This waits for the "modify" event to happen to the file named "filename". When that happens the inotifywait command outputs filename MODIFY (which we discard by sending the output to /dev/null) and then terminates, which causes the body of the loop to be entered.

Read the manpage for inotifywait for more possibilities.

Without inotifywait you can use this little script and a cron job (every minute or so):

#!/usr/bin/env bash

#

# Provides      : Check if a file is changed

# 

# Limitations   : none

# Options       : none

# Requirements  : bash, md5sum, cut

# 

# Modified      : 11|07|2014

# Author        : ItsMe

# Reply to      : n/a in public

#

# Editor        : joe

#

#####################################

#

# OK - lets work

#



# what file do we want to monitor?

# I did not include commandline options

# but its easy to catch a command line option

# and replace the defaul given here

file=/foo/bar/nattebums/bla.txt



# path to file's saved md5sum

# I did not spend much effort in naming this file

# if you ahve to test multiple files

# so just use a commandline option and use the given

# file name like: filename=$(basename "$file")

fingerprintfile=/tmp/.bla.md5savefile



# does the file exist?

if [ ! -f $file ]

    then

        echo "ERROR: $file does not exist - aborting"

    exit 1

fi



# create the md5sum from the file to check

filemd5=`md5sum $file | cut -d " " -f1`



# check the md5 and

# show an error when we check an empty file

if [ -z $filemd5 ]

    then

        echo "The file is empty - aborting"

        exit 1

    else

        # pass silent

        :

fi



# do we have allready an saved fingerprint of this file?

if [ -f $fingerprintfile ]

    then

        # yup - get the saved md5

        savedmd5=`cat $fingerprintfile`



        # check again if its empty

        if [ -z $savedmd5 ]

            then

                echo "The file is empty - aborting"

                exit 1

        fi



        #compare the saved md5 with the one we have now

        if [ "$savedmd5" = "$filemd5" ]

            then

                # pass silent

                :

            else

                echo "File has been changed"



                # this does an beep on your pc speaker (probably)

                # you get this character when you do:

                # CTRL+V CTRL+G

                # this is a bit creepy so you can use the 'beep' command

                # of your distro

                # or run some command you want to

                echo 

        fi



fi



# save the current md5

# sure you don't have to do this when the file hasn't changed

# but you know I'm lazy and it works...

echo $filemd5 > $fingerprintfile

Came looking for a one-liner on MacOS. Settled on the following. Compiled and added this tool to my path. This took less then 30 seconds.

$ git clone git@github.com:sschober/kqwait.git

$ cd kqwait

$ make

$ mv kqwait ~/bin

$ chmod +x ~/bin/kqwait

Next, I went to the directory in which I wished to do the watching. In this case, I wished to watch a markdown file for changes, and if changed issue a make.

$ while true; do kqwait doc/my_file.md; make; done

That's it.

You probably don't need to compare md5sum if you have the diff utility available.

if ! diff "$file1" "$file2" >/dev/null 2>&1; then

  echo "$file1 and $file2 does not match" >&2

  ## INSERT-YOUR-COMMAND/SCRIPT-HERE

  ## e.g. cp "$file1" "$file2"

fi

the ! negates e.g. true if the statement is false

Caveat is you need the original file to compare with diff which (imo) the same as what md5sum script is doing above.

You can try entr command-line tool, e.g.

$ ls file1 | entr beep

if you are checking changes in a git repo, you can use:

#!/usr/bin/env bash



diff="$(git diff | egrep some_file_name_or_file_path | cat)"



if [[ -n "$diff" ]] ; then

    echo "==== Found changes: ===="

    echo "diff: $diff"

    exit 1

else

    echo 'Code is not changed'

fi

Done in 2 steps Tested and worked fine in both scenarios

a. cp orginalfile fileneedto_be_changed'(Need to do only one Time)

orginalfile=====>which supposed to be changed

b.

differencecount=`awk 'NR==FNR{a[$0];next}!($0 in a){print $0}' orginalfile fileneedto_be_changed|wc -l`



if [ $differencecount -eq  0 ]

then

echo "NO changes in file"

else

echo "Noted there is changes in file"

fi