However, it's critical that $! be "emptied"

It's not critical at all - I've already mentioned that undefining $! is a useless, almost redundant operation, consequetive operations will clear and set a previously set $! if they need to.

As in the following example, "gobbledegook" is a non-existant file. 

$ perl -le 'open F, "gobbledegook" or print "WARN1: $!"; print "PRINT:
+ $!"; readlink "test" or print "WARN2: $!";  print "PRINT: $!'
WARN1: No such file or directory
PRINT: No such file or directory
WARN2: Invalid argument
PRINT: Invalid argument

[download]
It's quite clear here that the currency or validity of $! after a system call is unaffected by it's previous state, it's just another global variable.

I have reason to believe that some perl programmers undefine $! after a system call wherein they do not check or cannot check the return value or because $! wasn't localized during that operation. E.g. After a use; statement 
$ perl -e 'print "BANG: $!"'
BANG:

$ perl -Mstrict -e 'print "BANG: $!"'
BANG: Bad file descriptor

[download]

In reply to Re^5: Best way to handle readline errors? by Firefly258
in thread Best way to handle readline errors? by jrw

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.