Ruby is a direct descendant of Perl and borrows its regex syntax.

Ruby used Oniguruma (and now Onigmo) for RegEx https://github.com/k-takata/Onigmo

Yes (well, for MRI at least; I'm not sure other implemebtations use the same regex engine) and it used a different regex engine before Oniguruma. But engines and syntax are unrelated; Ruby has a dedicated regex literal syntax which was directly inspired by Perl.

As far as I can make out these regex engines are very close to Perl5.

Javascript has regex literals

    /foo\sbar/i;

Is the same as:

    new RegExp('foo\\sbar', 'i');

One thing that annoys me a bit about the JS syntax though: As far as I know, JS regexp literals don't have custom delimiter support. For instance in perl you can do this:

    $str =~ m{/some/path/\w+}

But in JS you need to escape the / characters, or use a normal string as an argument to Regexp, in which case you need to escape the backslashes:

    /\/some\/path\/\w+/
    Regexp("/some/path/\\w+")

Some other languages have a "raw string" syntax which disables backslash processing. For instance, Python (see https://docs.python.org/3/library/re.html and https://docs.python.org/3/reference/lexical_analysis.html#st...) and Rust (see https://doc.rust-lang.org/reference/tokens.html#raw-string-l...).

> Perl is still the only language I've seen that has a dedicated syntax for regular expressions.

So, you've never seen Ruby?

I've done a very small about of ruby programming which did not involve regular expressions.

Javascript is like Perl: /foo/i.test('foobar') is valid JS.