If you need to do it "with regular expressions", then review your course material on regular expressions.

What code have you already written?

What is your code supposed to do, in separate steps?

How does your code fail to do what you want?

Maybe working on some examples in ascending difficulty helps you solve your problem:

Solve the problem of "reversing" for

  1. abcdef
  2. 123456
  3. 123456abcdef
  4. abcdef123456
  5. abcdef123456abcdef
  6. 123456abcdef123456
  7. 123456abcdef123456abcdef123456abcdef123456

Also review perlre and perlretut.

In reply to Re^5: Reverse fraction of a string by Corion
in thread Reverse fraction of a string by Bintuch

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.