I'm wondering if it's efficient to open close the file each time, the handle could be kept in the closure. And flock would cover problems with concurrent use.

Opening and closing each time is indeed less efficient. Keeping the file open would require a lock-seek-write-flush-unlock sequence, which introduces more complexity, and given that the OP is debugging "weird" behavior, I thought it best to give the simpler, albeit less efficient, method that uses only simple filesystem operations. I perhaps should have clairifed that my suggestion is one for debugging and not for high-performance logging. (Also, I seem to remember that keeping the file open does not work on Windows when multiple processes are accessing it, though I'm not yet sure whether that's the case here.)

In reply to Re^3: Why can't some of my modules do log output to a file? by haukex
in thread Why can't some of my modules do log output to a file? by LittleJack

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.