Re: File Access + Thread Safe
yitzle wrote: I got a CGI script that is being used by multiple users. It reads/writes data to a database (text file). When it reads, it reads the entire file, and when it writes, it tuncrates and rewrites the entire file. Can/will this screw up the file if two people try to write to the file at the same time? How do I prevent problems? (SQL/MySQL is not an option) perldoc -q \block 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 -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
cpanplus module cyclic dependency
Hi, I tried to install CPANPLUS with my cpan module. The installation ended with the following error: Recursive dependency detected:s/Autoflush.pm blib/lib/CPANPLUS/Internals/Utils/ACPANPLUS - K/KA/KANE/CPANPLUS-0.78.tar.gzb/lib/CPANPLUS/Module/Fake.pm - CPANPLUS::Shell::Defaultb/lib/CPANPLUS/Error.pm - K/KA/KANE/CPANPLUS-0.78.tar.gz..pm blib/lib/CPANPLUS/Internals/Constants.pm Cannot continue.Dist/Base.pm blib/lib/CPANPLUS/Dist/Base.pm I am tring to install cpanplus on a cygwin. Has anyone a clue for that? Best regards, Yaron Kahanovitch -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
testing return values
Hiya. I'm looking for the correct Perl style for testing and storing
a return value in a control statement. The solution in any other
language is pretty obvious, but I get the distinct impression that
there's a 'right' way in Perl...
Let's say I want to test a scalar returned from a subroutine, and
also keep a copy for my own use:
$scalar = sub( $argument );
if( $scalar ){
}
Naturally that's no big deal. Now let's say I have a tree I want to
traverse, or some similar open-ended thing to evaluate, and want to
run it until a condition is reached..
while( read_tree( $argument ){
}
Again no biggie. The problem is if I want to keep the result.
Obviously I can't do this:
while( $tree_element = read_tree( $argument ) ){
do_something( $tree_element );
}
I can come up with a brute-force solution of course, but there's
probably a better, Perlish way that I'm not aware of. In addition, I
don't expect a return value from some module to be consistently
undefined or zero; it could change under some circumstances. This
makes me think that the problem has been dealt with long ago, and
just doesn't stick out in the llama/alpaca/whatever books.
Hopefully I explained this correctly!
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/
Re: testing return values
Now, why can't you do this?
while( $tree_element = read_tree( $argument ) ){
do_something( $tree_element );
}
I would certainly use it. In C this is called operation overflow or something...
On 4/22/07, Mike Lesser [EMAIL PROTECTED] wrote:
Hiya. I'm looking for the correct Perl style for testing and storing
a return value in a control statement. The solution in any other
language is pretty obvious, but I get the distinct impression that
there's a 'right' way in Perl...
Let's say I want to test a scalar returned from a subroutine, and
also keep a copy for my own use:
$scalar = sub( $argument );
if( $scalar ){
}
Naturally that's no big deal. Now let's say I have a tree I want to
traverse, or some similar open-ended thing to evaluate, and want to
run it until a condition is reached..
while( read_tree( $argument ){
}
Again no biggie. The problem is if I want to keep the result.
Obviously I can't do this:
while( $tree_element = read_tree( $argument ) ){
do_something( $tree_element );
}
I can come up with a brute-force solution of course, but there's
probably a better, Perlish way that I'm not aware of. In addition, I
don't expect a return value from some module to be consistently
undefined or zero; it could change under some circumstances. This
makes me think that the problem has been dealt with long ago, and
just doesn't stick out in the llama/alpaca/whatever books.
Hopefully I explained this correctly!
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/
Re: testing return values
Mike Lesser wrote:
Hiya. I'm looking for the correct Perl style for testing and storing a
return value in a control statement. The solution in any other language
is pretty obvious, but I get the distinct impression that there's a
'right' way in Perl...
Let's say I want to test a scalar returned from a subroutine, and also
keep a copy for my own use:
$scalar = sub( $argument );
if( $scalar ){
}
Naturally that's no big deal. Now let's say I have a tree I want to
traverse, or some similar open-ended thing to evaluate, and want to run
it until a condition is reached..
while( read_tree( $argument ){
}
Again no biggie. The problem is if I want to keep the result. Obviously
I can't do this:
while( $tree_element = read_tree( $argument ) ){
do_something( $tree_element );
}
I can come up with a brute-force solution of course, but there's
probably a better, Perlish way that I'm not aware of. In addition, I
don't expect a return value from some module to be consistently
undefined or zero; it could change under some circumstances. This makes
me think that the problem has been dealt with long ago, and just doesn't
stick out in the llama/alpaca/whatever books.
Hopefully I explained this correctly!
while (my $x = func()) {
:
}
is perfectly valid. In Perl every operator returns a value, and the assignment
operator is no exception. It's value is the expression on the left of the equals
sign, and it's even an lvalue so you can do things like
($x = 3)++;
leaving $x with a value of four. This sort of thing is more useful for things
like
$p = $q = 'A';
which is the same as
$p = ($q = 'A');
or
$q = 'A'; $p = $q;
But the bottom line is that your while loop is quite valid.
HTH,
Rob
--
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
http://learn.perl.org/
