Each instance would be trying to process the same files.
Oh. I never got the impression that the OP wanted this. I fail to see why that's a benefit.
Which would mean lots of "file in use" errors and/or duplicated results.
Windows doesn't allow two processes to open the same file? That sounds like an easy DoS.
The multiple instances would be trying to redirect their output to the same file. Even if you use append (>>), Windows won't let you do that. Not sure if *nix will?
Unix allows multiple processes to write to the same file. And if the file is opened in append mode, all write()s will go to the end of the file.

In reply to Re^3: Search through multiple files and output results to new file by JavaFan
in thread Search through multiple files and output results to new file by Moloch

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.