How to replace a lower case in a regular expression without touching the corresponding capital?

Question

PHP

There is this code:

if (условие) $i = preg_replace('/https:\/\/site.com\/([^\s]*)a.jpg/U','https://site.com/$1b.jpg',$i);

As you can see, with a certain if, the letter a at the end of the file name is changed to the letter b .

The problem is that the capital letter also changes if it is at the end of the file - A . But this cannot be allowed.

How can I make a letter change only if it is lowercase?

Thanks in advance to all who answer!

Answer 1

This is how it works by default.

print preg_replace('/https:\/\/site.com\/([^\s]*)a.jpg/U','https://site.com/$1b.jpg', 'https://site.com/testa.jpg');
// https://site.com/testb.jpg

print preg_replace('/https:\/\/site.com\/([^\s]*)a.jpg/U','https://site.com/$1b.jpg', 'https://site.com/testA.jpg');
// https://site.com/testA.jpg