Question

What is the regular expression that can match the following 2 strings.

Hi<Dog>Hi and <Dog> in a given text.

Update:

What regex will match this one?

<FONT FACE="Verdana" SIZE="16" COLOR="#0B333C" LETTERSPACING="0" KERNING="0">If you access the web site click the link below:<FONT SIZE="12"></FONT></FONT>

<FONT.*?<\/FONT> matches only till the first </FONT>

Answer 1

The pattern ^([a-z]*)<[A-Z]*>\1$ will match these strings (as seen on rubular.com):

ab<XYZ>ab
<XYZ>
bleh<FOO>bleh
<>

It will not match these:

ab<XYZ>de
x<XYZ>y
FOO<foo>FOO

That is, the pattern is something like

tag<CONTENT>tag

The same tag appears for both the “prefix” and the “suffix”. Tag consists of zero or more lowercase letters. Content consists of zero or more uppercase letters. The prefix part is matched and captured by group 1, and then a backreference \1 is used to match that string again for the suffix.

The […] is a character class. Something like [aeiou] matches one of any of the lowercase vowels. [^…] is a negated character class. [^aeiou] matches one of anything but the lowercase vowels.

As a Java string literal, the pattern is "^([a-z]*)<[A-Z]*>\\1$".