I usually use XML::XSH2 for XML manipulation. In this case, I needed to wrap your input file into <xml>...</xml> and to add _ between subject and names to make it a valid XML. The output is also different to your expected output: spaces between attributes are not optional in XML. 
my $input := open 935956.xml ;
my $student_hash := hash concat(@name, '#', @number) $input/xml/data/s
+tudent ;
my $semister_hash := hash ../@number $input/xml/data/semister/@subject
+_names ;

my $out := create xml ;
for my $university in $input/xml/university {
    my $new_uni := cp $university into $out/xml ;

    for my $student in $new_uni//student {
        cp xsh:lookup('student_hash', concat($student/@name, '#', $stu
+dent/@number))/@address into $student ;
        for $student/semester cp xsh:lookup('semister_hash', ./@number
+) into . ;
    }
}

save :f 935956-out.xml $out ;

[download]

In reply to Re: help me with perl script that add xml attritutes by choroba
in thread help me with perl script that add xml attritutes by veerubiji

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.