I imagine there's a more efficient way to do this with backwards or forwards looking, but I'm not that good at regex. The following works, even if it does more substitutions than are necessary: 
$_ = join '', <DATA>;

# Add & to front of function calls without.
s/&?(\w+\(.*?\))/&$1/g;

# Add () to end of function calls without.
s/(&\w+)(?:\((.*?)\))?/$1($2)/g;

print;

__DATA__
&somesub('args');
somesub('args');
&somesub;

[download]
This way of doing things may have problems, however. You will end up not only replacing sub calls, but built-in function calls as well. You need to add a sub to check function names against a Perl function list, and add that to the regex with an e flag.

In reply to Re: Regex to add text if text is missing by TedPride
in thread Regex to add text if text is missing by bradcathey

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.