How to detect modified files across two directories

Suppose you have two directories old and new containing the same files, but some of them have changed in the new directory. Further suppose that source control is not used This post explains how to detect the modified files based on their MD5 sums through a simple bash script.

For this example, suppose the file types we are interested in are Python scripts (.py files). Note that we define the variables NEW_DIR and OLD_DIR (representing the paths to the new and the old directories, respectively) using absolute paths (i.e. paths that start from the root of the filesystem).

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#!/usr/bin/bash

NEW_DIR="/path/to/new"
OLD_DIR="/path/to/old"

cd $NEW_DIR
files=`find . -name "*.py"`
for file in $files ; do
    filename=`echo $file | sed 's/\.\///g'`
    orig="${OLD_DIR}/${filename}"
    md5_orig=`md5sum $orig | awk '{ print $1 }'`
    md5_new=`md5sum $file | awk '{ print $1 }'`
    if [[ "${md5_orig}" != "${md5_new}" ]] ; then
        echo $file $md5_orig $md5_new
    fi
done

In lines 6-7, we search for all the files ending in .py in the $NEW_DIR. For each matching file, we transform its filename into orig, i.e. the corresponding path and file name in the $OLD_DIR (lines 9-10). We then compute the MD5 sum of the two files (lines 11-12) and display only files where the MD5 sums differ (lines 13-15).