re = /(?s)<(category) name="Content Server Categories:(.+?)">(.+?)<\/(category)>/m
str = '<category name="Content Server Categories:FOLDER:test category">
<attribute name="test attribuut"><![CDATA[test]]></attribute>
<attribute name="test attribuut1"><![CDATA[test1]]></attribute>
</category>
<category name="Content Server Categories:FOLDER1:FOLDER2:test category">
<attribute name="test attribuut"><![CDATA[test]]></attribute>
<attribute name="test attribuut1"><![CDATA[test1]]></attribute>
</category>
<category name="Content Server Categories:FOLDER NAME:test category">
<attribute name="test attribuut"><![CDATA[test]]></attribute>
<attribute name="test attribuut1"><![CDATA[test1]]></attribute>
</category>
<category name="Content Server Categories:FOLDER NAME: FOLDER NAME1:test category">
<attribute name="test attribuut"><![CDATA[test]]></attribute>
<attribute name="test attribuut1"><![CDATA[test1]]></attribute>
</category>
<category name="Content Server Categories:FOLDER:test category name">
<attribute name="test attribuut"><![CDATA[test]]></attribute>
<attribute name="test attribuut1"><![CDATA[test1]]></attribute>
</category>'
subst = '<$1-$2 name="Content Server Categories:$2">$3</$1-$2>'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html