note
erikharrison
<p><i>On *nix, the value returned by system doesn't necessarily reflect an OS error</i></p>
<p>Which is a common newbie error. They check the value of $! inappropriately after [system]. According to perlvar, $! (or $^E on some systems) will have useful information after [system] or backticks if (and only if) $? == -1. Hence the check.</p>
<p><i>What distinct information is available on exit from a VMS, Win32 or OS/2 system call? How much different are the extended error returns?</i></p>
<p>[system] returns the same. However, [system] may fail with $? = -1 when the child process fails due to an OS error. $! is C's errno, but on VMS, Win32, and OS/2 the underlying API provides it's own error messages which C's errno does not reflect. On these systems $^E holds that value (see perlvar for the specific API calls made to get that value). This is a workaround for the fact that Perl and C are still a bit *nix centric. $^E exists for people who aren't on *nix systems while still allowing *nix programmers on Windows or the like still get what they expect from $!.</p>
<p>Cheers,<br>
Erik
<p><i>Light a man a fire, he's warm for a day. Catch a man on fire, and he's warm for the rest of his life. - Terry Pratchet</i></p>
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