How to get `grep` to emit the right side of 'URL=http://example.com'?

So I'm trying to grep the following file myfile.txt:

[Section]
URL=http://example.com

I want it to return everything after the URL=, so only http://example.com.

If I try any of the following, they do not work:

>grep -m1 -i 'url=' myfile.txt
URL=http://example.com
>grep -m1 -i 'http.+*' myfile.txt
URL=http://example.com
>grep -m1 -i -o 'http\.$' myfile.txt

>grep -m1 -i -o 'http\.*' myfile.txt
http
>grep -m1 -i -o 'http\.*$' 
>

How can grep emit everything to the right of the equals symbol? It seems to refuse to match to the end of the line. And this will fail if the address happens to be anything other than 'http' (such as FTP, etc.)

Additions:

This is on Mabox (Manjaro, Arch) Linux.
It might very well be possible with some specialized Mabox tool; however general GNU tools are assumed because the answer might apply to anyone else finding this question, such as on Alpine. So I'd prefer an answer to be general, and not platform-specific.
grep was chosen simply because it should be possible, and easily emits a full matched line. grep claims to support regular expressions, so should be able to match to end-of-line. If another command would work better and/or simpler, that is fine; grep does not have to be used. But a standard command that works on the vast majority of Linuxes would be most helpful to others.

Solution

Instead of grep, have you considered sed?

Given your sample input file, this command...

sed -n '/^URL=/ s/.*=//p' myfile.txt

Produces as output:

http://example.com

Or maybe awk:

awk -F= '/^URL=/ {print $2}' myfile.txt

The problem with grep in this instance is that it's primarily a tool for returning matched lines; it's not really meant for performing transformations on those matches.

The -o option is an interesting idea, but there's not really anyway to restrict it to match only the part after the = unless you prefilter the input like this:

grep '^URL=' myfile.txt | grep -o '[^=]*$'