Thanks John for your quick answer.
what you said about:
>Only the $? variable applies to the system() function. I think that
>'del' is an internal command.com function (I haven't used DOS/Windows
>in a long time) so $? will probably report the return status of
> command.com?
...seems to be true:
This is what is reported if the file 'pepe.txt' does not exist using
'system()':
"
BEFORE:
-----
$@ is -><-
$! is -><-
$^E is -><-
$? is ->0<-
Could Not Find G:\Oscar\Computing\Perl\Proyectos\PCshutdownScript\pepe.txt
(above a normal system error from 'del' command, I guess)
AFTER:
----
$@ is -><-
$! is ->No such file or directory<-
$^E is ->The system cannot find the file specified<-
$? is ->256<- (The value is not 0)
"
... and this is what is reported when the file 'pepe.txt' does not exist
using 'open':
"
BEFORE:
-----
$@ is -><-
$! is -><-
$^E is -><-
$? is ->0<-
AFTER:
----
$@ is -><-
$! is ->No such file or directory<-
$^E is ->The system cannot find the file specified<-
$? is ->0<-
Could Not Find G:\Oscar\Computing\Perl\Proyectos\PCshutdownScript\pepe.txt
"
...but - What happens if I use 'open'? I cannot see any difference if the
file 'pepe.txt' exists or not :-?
This is what is reported when the file 'pepe.txt' exists using 'open':
"
BEFORE:
-----
$@ is -><-
$! is -><-
$^E is -><-
$? is ->0<-
AFTER:
----
$@ is -><-
$! is ->No such file or directory<-
$^E is ->The system cannot find the file specified<-
$? is ->0<-
"
:-?
Using 'open' I cannot say if the 'del' command was done correctly or not,
although there is a message probably to STDERR that I do not know how to
manage. :-(
So far, I use 'open' a lot because if I open a file I can manage the
information using the file handler.
Answering your question to 'Do you want to handle errors or do you want to
report errors?'
I would like to handle the errors and I thought using these variable would be a
good method, wouldn't be?
Thanks again.
"John W. Krahn" <[EMAIL PROTECTED]> wrote:
oscar gil wrote:
> Hello everybody,
Hello,
> I wanted to learn a bit more about how to handle errors when I am
> working with files,
Do you want to handle errors or do you want to report errors?
> so I wrote this simple script to start with it
> where you can see that first I show the normal perl errors variables,
> then I try to delete a file and finally I show the errors variables
> again.
> The file I try to delete exists and it is at the same directory and
> after the script the file is deleted, so it works.
> What surprised me is that at the end of the script the '$!' is 'No such
> file or directory' and '$^E' is 'The system cannot find the file
> specified' though the file was deleted correctly, :-?.
>
> My idea was to treat the '$!' when I am working with files but with
> this results I don't see how.
Have you read the documentation for the variables you are using?
perldoc perlvar
$CHILD_ERROR
$? The status returned by the last pipe close, backtick ()
command, successful call to wait() or waitpid(), or from
the system() operator. This is just the 16-bit status
word returned by the wait() system call (or else is made
up to look like it). Thus, the exit value of the
subprocess is really ("$? >> 8"), and "$? & 127" gives
which signal, if any, the process died from, and "$? &
128" reports whether there was a core dump.
(Mnemonic: similar to sh and ksh.)
$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:
$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 $!.
[ SNIP ]
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.)
$EVAL_ERROR
$@ The Perl syntax error message from the last eval()
operator. If $@ is the null string, the last eval()
parsed and executed correctly (although the operations
you invoked may have failed in the normal fashion).
(Mnemonic: Where was the syntax error "at"?)
> Let me tell you I am using this version of perl with Windows and I
> tried it both, Win2k and WinXP:
> This is perl, v5.8.7 built for MSWin32-x86-multi-thread
> (with 14 registered patches, see perl -V for more detail)
>
> Here it is the script and afterwards there is the STDOUT exit.
>
> ----------------------------------------------------
> #!/usr/bin/perl -w
> use strict;
>
> print "\n\n\nBEFORE:\n-----\n";
> print '$@'." is ->$@<-\n";
> print '$!'." is ->$!<-\n";
> print '$^E'." is ->$^E<-\n";
> print '$?'." is ->$?<-\n\n\n";
>
> # I tried with open and with system()
> #open (RD , "del pepe.txt |") or die "I cannot RD\n";
Only the $! or $^E variables apply after open() *FAILS*. If open()
completed successfully then the values of $! and $^E are meaningless.
> system ("del pepe.txt");
Only the $? variable applies to the system() function. I think that
'del' is an internal command.com function (I haven't used DOS/Windows in
a long time) so $? will probably report the return status of command.com?
[ SNIP ]
> Questions:
>
> 1.- Why a have the '$!' and '$^E' set as it could not find the file
> when in reality it could?
Because the values of $! and $^E are only valid after an error occured.
> I tried with 'system()' and with 'open' with the same results. :-(
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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