A good place to start is with the perlre documentation. It is fairly extensive, but is likely to be much more useful to you in the long run than me decomposing the expression I gave above. Note that there is a very useful "See Also" section at the bottom of the documentation - in fact you might want to check that out first. There is a trick that may help you break the regex down into easier to understand parts though:

$str =~ s/
    (^|\n)
    [\n\s]*
    /$1/gx;

[download]

The x switch ignores white space (including new lines) so we can use white space to break up the parts of the regex into units.

Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond

In reply to Re^3: Removing empty line(s) with regex in a multiple strings in a variable by GrandFather
in thread Removing empty line(s) with regex in a multiple strings in a variable by monkfan

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.