Can someone help explain this code? It is a shell script for creating a checksum list - sql

Question

#!/bin/bash
# create a list of checksums
cat /dev/null > MD5SUM
for i in */*/*.sql ; do test -e $i && md5sum $i >>MD5SUM ; done
Then this command is used to check to see if anything has changed:
md5sum -c MD5SUM
It works fine and everything. I just don't really understand how. Say if I wanted to make a checksum list of all the files in my home directory $HOME how can I do that? What does the */*/*.sql part of the for loop mean? I'm assuming that is to display SQL files only but how can I modify that? Say I wanted all files in the directory? Why is it not just *.sql ? What does the rest of the for loop do in this case?

Answer 1

Lets go by parts:
cat /dev/null > MD5SUM
this will only "erase" the previous MD5SUM file/list that was created before.
for i in */*/*.sql;
this will iterate over files that are 2 directories deep from your current folder. If you have folders
~/a/b
~/c/d
~/e/f
and you run your script in your home folder (~) all "*.sql" inside directories b,d,f will have the checksum calculated and piped to a file MD5SUM in the current direcotry:
do test -e $i && md5sum $i >>MD5SUM ; done
Now Answering your questions:
Say if I wanted to make a checksum list of all the files in my home directory $HOME how can I do that?
I would use the find command with the exec option
find $HOME -maxdepth 1 -name \*.sql -exec md5sum {} \;
What does the //*.sql part of the for loop mean?
I answered it above, anyway only goes 2 directories deep before getting to the files.
I'm assuming that is to display SQL files only but how can I modify that? Say I wanted all files in the directory?
Change
for i in */*/*.sql;
to
for i in */*/*;
or for current directory
find $HOME -maxdepth 1 -name \* -exec md5sum {} \;
Why is it not just *.sql ? What does the rest of the for loop do in this case?
Explained before.
Hope it helps =)