One way to read those strings.

If you like your code un-obfuscated and easy to understand: :P

The ls isn't needed as fileglobbing will do it. ( and you are using file globbing anyway with *.jpg).

Also, he just wants to process files with the pattern IMG*.jpg. *.jpg will process all *.jpg files.

The "s" in "files" indicates plurality. But I probably should have used "pictures" instead of file. Using the word "file" has become a habit. I use it for oneliners in for loops working in the shell as well.

Using LAST in place of ${#ARRAY[@]} is a good idea for readability but the form of the for loop I used resembles C and is given if you enter "help for". I don't think using $LAST in the loop would precompute the value of LAST however. That would be the case in C. However, the name "LAST" indicates that it is the last element. Then you decrement it. That adds confusion it itself.
The letter "n" is commonly used to indicate an index. The ${#files[@]} was the only obfuscated part and should have been commented in the code.

Perhaps I should have added comments to the code instead of putting them at the end of the message.

If I have a saving grace, it's that I created a bunch of files matching the filepattern and tested the program before posting. Instead of images, IMG1000.jpg contained the text "IMG1000.jpg". So after the renaming, I cat'ed out the contents of the files to prove that the reordering took place.

The ls isn't needed as fileglobbing will do it. ( and you are using file globbing anyway with *.jpg).
Just part of the un-obfuscating. Which is more easy to understand?
ARRAY=( $(ls -1 *.jpg) )
ARRAY=( *.jpg )
Maybe just a mater of preference. And I thought ls -1 IMG[0-9][0-9][0-9][0-9].jpg just looked ugly.

The "s" in "files" indicates plurality. But I probably should have used "pictures" instead of file. Using the word "file" has become a habit. I use it for oneliners in for loops working in the shell as well.

I used ARRAY because I was creating an ARRAY. I have no rhyme or reason for the things I do.

If I have a saving grace, it's that I created a bunch of files matching the filepattern and tested the program before posting. Instead of images, IMG1000.jpg contained the text "IMG1000.jpg". So after the renaming, I cat'ed out the contents of the files to prove that the reordering took place.
Yeah I did the exact same thing only mine were named like my camera names them (which explaines the pic000.img. Funny thing is the middle file never gets changed

BTW: I was joking and referring to the perl script, because as everyone knows nothing beats perl for obfuscating!

Using the ls is like preceding grep or sed with cat. It isn't un-obfuscating, it's a bad habit.

I'll compromise on the ARRAY, but it shouldn't be in capital letters because capital letters are used in bash to indicate constants. A name like picture_array or pic_array would be better. It communicated the type and what the elements are.

Ditto for FIRST and LAST. It looked strange when you started changing them.

1. You really need to chill.
2. Please don't attempt to correct my scripting style (old dog new trick sort of thing.)
3. Have a good day.

<mental note> Human race becoming more humorless and up tight.</mental note>

only for people who don't speak perl

actually, it doesn't really matter. You can keep telling people not to use cat because its UUOC, or whatever, in the end, people will still UUOC. Even books that are published (yes , I saw one just now at the bookshop using UUOC ) You can tell people not to use capital letters for whatever reasons, but people will still use it. Its just a matter of choice, when that choice is presented to them. If bash could restrict the use of capital letters just for constants, then people won't be able to use capital letters as variables. but the bash people who created bash doesn't really think about that...you can tell people that Perl is the king of obfuscation, but people still use them, cause once again, the key to this => choice.

only for people who don't speak perl
I once studied a perl script to see if I could learn from it. I learned that perl is a "self encrypting language!" :P

People will ultimately do what they want (assuming it's syntactically legal), but it doesn't hurt to (gently) encourage them to do it better, especially if there's a danger of them doing it in prod where it will confuse/annoy everbody else.
There is a such a concept as 'best practice'.

rubbish! you just need to be a retentive weirdo freak to enjoy it!