md5sum myfile.php > myfile.php.md5
Above command will generate md5 checksum of file myfile.php and store in file myfile.php.md5. myfile.php.md5 can be used to verify integrity of file anytime.
If we want to generate md5sum of a file named index.php. Use the following command to do it and store generated md5 value of file in index.php.md5 file.
# md5sum index.php > index.php.md5
Now in future we can use index.php.md5 to verify integrity of file using following command. This command will show output as OK or FAILD.
# md5sum -c index.php.md5