IIRC $! is only in a defined state after a failed system call, though there might be a few places where perl or some module sets it to zero before a system call. If the last system call didn't fail, $! is not guaranteed to be zero - it may have any value and its value is without defined meaning.

man 3 errno on my CentOS system says:

The <errno.h> header file defines the integer variable errno, which is set by system calls and some library functions in the event of an error to indicate what went wrong. Its value is significant only when the call returned an error (usually -1), and a function that does succeed is allowed to change errno.

Thus one of the possibilities you should consider is that the last system call succeeded but left errno with a non-zero value. Another possibility is that the last system call (or the last N system calls) all succeeded without changing the value of errno and it still has the value set from either the immediately preceding failed system call (which should have set it) or some subsequent successful system call. In other words, it might be quite difficult to determine which system call set it.

In reply to Re: "use strict" sets $! by ig
in thread "use strict" sets $! by rovf

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.