Question

I’m wondering how can I replace a character with another in a big string, only if the match is between { }

This:

bla bla % bla {ok text %nothing} some {% more} % text {yes %no ok} ok

To this:

bla bla % bla {ok text ^^nothing} some {% more} % text {yes ^^no ok}
ok

Notice the {% more} wasn’t changed because there was a space between the character and the letter.

Your is much appreciated.

Answer 1

If {} are not nested and no } can occur outside of them, you can do things like:

preg_replace('/%(?=\w[^{]*})/', '^^', $string);

When the string is:

bla % bla {ok text %nothing} some {% more} % text {yes %no ok} ok { %foo %bar %baz }

you would get:

la % bla {ok text ^^nothing} some {% more} % text {yes ^^no ok} ok { ^^foo ^^bar ^^baz }

---

If nested {} are allowed, you could use:

%(?=\w([^{}]*+(?:{(?1)}[^{}]*+)*+)})

Which works as the first one, with the [^{]* being replaced by ([^{}]*+(?:{(?1)}[^{}]*+)*+), which is recursively checking for arbitrary nested {}.

Example:

$string = '%a { %a { %a } %a { { %a } %a } } %a { % %a } %a { %a }';
echo preg_replace('/%(?=\w([^{}]*+(?:{(?1)}[^{}]*+)*+)})/', '^^', $string);

Output:

%a { ^^a { ^^a } ^^a { { ^^a } ^^a } } %a { % ^^a } %a { ^^a }