AndrewMcHorney wrote:
Hello
Hello,
Is there a way in Perl to find out why a file failed to open? I am
working on a script that is opening and reading a lot of files. This
script is right now being written on a Windows based system.
perldoc perlvar
[ *snip* ]
$OS_ERROR
$ERRNO
$! If used numerically, yields the current value of the C
"errno" variable, or in other words, if a system or library
call fails, it sets this variable. This means that the
value of $! is meaningful only immediately after a failure:
if (open(FH, $filename)) {
# Here $! is meaningless.
...
} else {
# ONLY here is $! meaningful.
...
# Already here $! might be meaningless.
}
# Since here we might have either success or failure,
# here $! is meaningless.
In the above meaningless stands for anything: zero,
non-zero, "undef". A successful system or library call does
not set the variable to zero.
If used as a string, yields the corresponding system error
string. You can assign a number to $! to set errno if, for
instance, you want "$!" to return the string for error n, or
you want to set the exit value for the die() operator.
(Mnemonic: What just went bang?)
Also see "Error Indicators".
%! Each element of "%!" has a true value only if $! is set to
that value. For example, $!{ENOENT} is true if and only if
the current value of $! is "ENOENT"; that is, if the most
recent error was "No such file or directory" (or its moral
equivalent: not all operating systems give that exact error,
and certainly not all languages). To check if a particular
key is meaningful on your system, use "exists $!{the_key}";
for a list of legal keys, use "keys %!". See Errno for more
information, and also see above for the validity of $!.
$EXTENDED_OS_ERROR
$^E Error information specific to the current operating system.
At the moment, this differs from $! under only VMS, OS/2,
and Win32 (and for MacPerl). On all other platforms, $^E is
always just the same as $!.
Under VMS, $^E provides the VMS status value from the last
system error. This is more specific information about the
last system error than that provided by $!. This is
particularly important when $! is set to EVMSERR.
Under OS/2, $^E is set to the error code of the last call to
OS/2 API either via CRT, or directly from perl.
Under Win32, $^E always returns the last error information
reported by the Win32 call "GetLastError()" which describes
the last error from within the Win32 API. Most
Win32-specific code will report errors via $^E. ANSI C and
Unix-like calls set "errno" and so most portable Perl code
will report errors via $!.
Caveats mentioned in the description of $! generally apply
to $^E, also. (Mnemonic: Extra error explanation.)
Also see "Error Indicators".
John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall
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