ok so $? states CHILD_ERROR or last status returned by the last ` ....`
command.
$! states yields the current value of errno
in shell if I say it will give me a true or false value.
cat /tmp/foo
if [ $? -eq 0 ]
then
echo yes command succeeded
else
echo no.
fi
In Perl if I wanted to represent this I would use $! for any notification
of any failures such as opening a file. But when I add the code in red
specifically $? >> 8, I get a exit value of 2 and when I change it to $?
>> 127 I get a exit value of 0. I want to understand and know the code to
get a true (1) or false (0) value.
thanks,
For this situation assume linect is 3.
#!/usr/local/bin/perl -w
use strict;
use strict 'subs';
my $file = qq(/tmp/mbfree);
open (F, "+<$file") or die "unable to open file $file $!\n";
foreach (<F>) {
if ( $. < 2 ) {
last;
} else { print "linect is NOT less than 2: $. \n";
system ("cat /tmp/used");
my $exval = $? >> 8;
print "print exit value: $exval\n";
if ( $exval == 0 ) {
print "false, file open cat did not happen\n";
}else{
exit;
}
}
}
print "line count is: $. \n";
close (F);
derek,
"John W. Krahn"
<[EMAIL PROTECTED]
> To
Perl Beginners <beginners@perl.org>
02/27/2005 07:59 cc
PM
Subject
Re: return code
[EMAIL PROTECTED] wrote:
> All,
> am I using the correct method to get the return code whether a previous
> line or command was 0 false or 1 true?
>
>
> #!/usr/local/bin/perl -w
>
> use strict;
> use strict 'subs';
>
> my $file = qq(/tmp/mbfree);
> open (F, "+<$file") or die "unable to open file $file $!\n";
>
> foreach (<F>) {
> if ( $. > 2 ) {
> last;
> } else { print "return code is: $? \n";
> last;
> }
> }
> print "line count is: $. \n";
> print "return code is: $? \n";
> close (F);
perldoc perlvar
[snip]
$? The status returned by the last pipe close, backtick (``)
command, successful call to wait() or waitpid(), or from
the
system() operator. This is just the 16-bit status word
returned by the wait() system call (or else is made up to
look
like it). Thus, the exit value of the subprocess is really
("$? >> 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.)
Since you are not creating a child process, the $? variable does not
contain
any useful information.
John
--
use Perl;
program
fulfillment
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