Comment by neilk

In my experience `$` does reliably mean end of string for regular expressions, unless you specifically ask for "multiline" mode.

Ruby seems to be in multiline mode all the time?

    $ python -c 'import re; print "yes" if re.match(r"^[a-z ]+$", "foobar") else "no"'
    yes
    $ python -c 'import re; print "yes" if re.match(r"^[a-z ]+$", "foo\nbar") else "no"'
    no
    $ python -c 'import re; print "yes" if re.match(r"^[a-z ]+$", "foo\nbar", re.M) else "no"'
    yes

    $ perl -le 'print "foobar" =~ /^[a-z ]+$/ ? "yes" : "no"'
    yes
    $ perl -le 'print "foo\nbar" =~ /^[a-z ]+$/ ? "yes" : "no"'
    no
    $ perl -le 'print "foo\nbar" =~ /^[a-z ]+$/m ? "yes" : "no"'
    yes

    $ node -e 'console.log(/^[a-z ]+$/.test("foobar") ? "yes" : "no")'
    yes           
    $ node -e 'console.log(/^[a-z ]+$/.test("foo\nbar") ? "yes" : "no")'
    no            
    $ node -e 'console.log(/^[a-z ]+$/m.test("foo\nbar") ? "yes" : "no")'
    yes

    $ ruby -e 'if "foobar" =~ /^[0-9a-z ]+$/i then puts "yes" else puts "no" end'
    yes
    $ ruby -e 'if "foo\nbar" =~ /^[0-9a-z ]+$/i then puts "yes" else puts "no" end'
    yes

EDIT: this is documented behavior for Ruby. What other languages call multiline mode is the default; you're supposed to use \A and \Z instead. They do have an `/m` but it only affects the interpretation of `.`

https://docs.ruby-lang.org/en/master/Regexp.html#class-Regex...