I need to write some perl scripts for a class which include some for or foreach loops. For some reason even the simplest for loop are just returning a 500 server error. I've checked many times and the code also works on codepad.org, but I dont know why it is not working on the server.
I dont have access to the server logs so I can't really tell whats going on.
These are some very simple loops that are also causing the error.
#a=(2,3,4);
foreach my $r (#a) {
print $r;
}
or
#a=(2,3,4);
for ($i = 0; $i <= 2 ; $i++) {
print $a[$i];
}
Any ideas?
Any time you are writing a CGI script, put this at the top while you are working on it:
use CGI::Carp qw(fatalsToBrowser);
This will give redirect errors in your Perl script to the browser window. It should give you a better idea of what is causing your problem (assuming it is at the script level).
It also lets you easily send your own errors and test statements to the browser using die:
die "testing 1 2 3";
This can be useful for doing quick debugging.
Related
What is the best way to test a site with Perl? How can I emulate a lot of connections to check how my script works on heavy load? Maybe there is a nice module on CPAN?
I am not interested in testing for dead links or 404 errors, only in work speed.
I have written these before so I can help you but it seems pretty straight forward for example:
use LWP::Simple;
my #urls ;
while($in=<>) {
push #urls,$in ;
$start=time();
for (i=0;i++; i< 99999999) {
use LWP::Simple;
my $content = get $url;
die if (/error/ ~= $content) ;
## Decide if you want to look at anything else
}
$stop=time() ;
## Write a report
I am running a program in Perl that at one point evaluates data in an if statement called from within a subroutine, e.g.
sub check_good {
if (!good) {
# exit this subroutine
# restart program
}
else {
# keep going
}
} # end sub
The problem I have is with exiting and restarting. I know that I can just use exit 0; to exit straight out, but obviously this is not correct if I want to go back to the beginning. I tried calling the subroutine which essentially starts the program, but of course once it has run it will go back to this point again.
I thought about putting it in a while loop, but this would mean putting the whole file in the loop and it would be very impractical.
I don't actually know whether this is possible, so any input would be great.
If you have not changed #ARGV, or you keep a copy of it, you could possibly do something like exec($^X, $0, #ARGV).
$^X and $0 (or $EXECUTABLE_NAME and $PROGRAM_NAME, see Brian's comment below) are the current perl interpreter and current perl script, respectively.
An alternative would be to always have two processes: A supervisor and a worker.
Refactor all your logic into a subroutine called run(or main or whatever). Whn your real logic detect that it needs to restart it should exit with a predefined non-zero exit code (like 1 for example).
Then your main script and supervisor would look like this:
if (my $worker = fork) {
# child process
run(#ARGV);
exit 0;
}
# supervisor process
waitpid $worker;
my $status = ($? >> 8);
if ($status == 1) { ... restart .. }
exit $status; # propagate exit code...
In the simple scenario where you just want to restart once, this might be a bit overkill. But if you at any point need to be able to handle other error scenarios this method might be preferable.
For example if the exit code is 255, this indicates that the main script called die(). In this case you might want to implement some decision procedure wether to restart the script, ignore the error, or escalate the issue.
There are quite a few modules on CPAN implementing such supervisors. Proc::Launcher is one of them and the manual page includes a extensive discussion of related works. (I have never used Proc::Launcher, it is mainly due to this discussion I'm linking to it)
There's nothing to stop you calling system on yourself. Something like this (clearly in need of a tidy), where I pass in a command-line argument to prevent the code calling itself forever.
#!/usr/bin/perl
use strict;
use warnings;
print "Starting...\n";
sleep 5;
if (! #ARGV) {
print "Start myself again...\n";
system("./sleep.pl secondgo");
print "...and die now\n";
exit;
} elsif ((#ARGV) && $ARGV[0] eq "secondgo") {
print "Just going to die straightaway this time\n";
exit;
}
I have a server from which I can access a webpage. I want to test the server reaction when several users(say 60000 users) access the same webpage simultanously.
Im looking for a script to do this,a perl script will be better,
Here is the code I tried with
#!c:\\perl\\bin
use strict;
use WWW::Mechanize;
my $url = "http://www.cpan.org";
my $searchstring = "WWW::Mechanize";
my $mech = WWW::Mechanize->new();
while (i == 60000)
{
$mech->get($url);
i++;
}
But this scripts access the url 1 at a time, But I need simultanous access.
You can use ab. Use its concurrency (-c) and number of requests (-n) options.
Your code, as shown above, doesn't even compile. It would be far easier for people to help you if you gave us the exact code that you're using, rather than typing to retype it and adding typos.
To get your code to compile, I had to declare $i and add the $ before the two uses of i in your programme. I ended up with this:
#!/usr/bin/perl
use strict;
use WWW::Mechanize;
my $url = "http://www.cpan.org";
my $searchstring = "WWW::Mechanize";
my $mech = WWW::Mechanize->new();
my $i;
while ($i == 60000) {
$mech->get($url);
$i++;
}
You say that the loop only gets executed once. That's not true. The loop doesn't get executed at all. The condition on the loop is $i == 60000. The first time this condition is checked, $i is undefined so the condition is false and the loop is skipped.
I think you probably wanted $i <= 60000 instead.
But as Alan points out, you'd be far better off using an existing tool like ab.
You can either use Perl itself to launch your script 6000 times in parallel or write one (or maybe more than one) .BAT files or similar Windows scripting to launch the perl script.
Be careful to clearly understand how to execute stuff in detached mode under Windows.
(Of course you have to remove the while loop in your original script).
ab has already been mentioned, but that only tests against the root page (/) of the site. We found siege more useful in replicating real load, since we were able to test against a long list of URLs (10,000 or so) taken from our live access log...
Is there a Perl module which can test the CGI output of another program? E.g. I have a program
x.cgi
(this program is not in Perl) and I want to run it from program
test_x_cgi.pl
So, e.g. test_x_cgi.pl is something like
#!perl
use IPC::Run3
run3 (("x.cgi"), ...)
So in test_x_cgi.pl I want to automatically check that the output of x.cgi doesn't do stupid things like, e.g. print messages before the HTTP header is fully outputted. In other words, I want to have a kind of "browser" in Perl which processes the output. Before I try to create such a thing myself, is there any module on CPAN which does this?
Please note that x.cgi here is not a Perl script; I am trying to write a test framework for it in Perl. So, specifically, I want to test a string of output for ill-formedness.
Edit: Thanks
I have already written a module which does what I want, so feel free to answer this question for the benefit of other people, but any further answers are academic as far as I'm concerned.
There's CGI::Test, which looks like what you're looking for. It specifically mentions the ability to test non-Perl CGI programs. It hasn't been updated for a while, but neither has the CGI spec.
There is Test::HTTP. I have not used it, but seems to have an interface that fits your requirements.
$test->header_is($header_name, $value [, $description]);
Compares the response header
$header_name with the value $value
using Test::Builder-is>.
$test->header_like($header_name, $regex, [, $description]);
Compares the response header
$header_name with the regex $regex
using Test::Builder-like>.
Look at the examples from chapter 16 from the perl cookbook
16.9. Controlling the Input, Output, and Error of Another Program
It uses IPC::Open3.
Fom perl cookbook, might be modified by me, see below.
Example 16.2
cmd3sel - control all three of kids in, out, and error.
use IPC::Open3;
use IO::Select;
$cmd = "grep vt33 /none/such - /etc/termcap";
my $pid = open3(*CMD_IN, *CMD_OUT, *CMD_ERR, $cmd);
$SIG{CHLD} = sub {
print "REAPER: status $? on $pid\n" if waitpid($pid, 0) > 0
};
#print CMD_IN "test test 1 2 3 \n";
close(CMD_IN);
my $selector = IO::Select->new();
$selector->add(*CMD_ERR, *CMD_OUT);
while (my #ready = $selector->can_read) {
foreach my $fh (#ready) {
if (fileno($fh) == fileno(CMD_ERR)) {print "STDERR: ", scalar <CMD_ERR>}
else {print "STDOUT: ", scalar <CMD_OUT>}
$selector->remove($fh) if eof($fh);
}
}
close(CMD_OUT);
close(CMD_ERR);
If you want to check that the output of x.cgi is properly formatted HTML/XHTML/XML/etc, why not run it through the W3 Validator?
You can download the source and find some way to call it from your Perl test script. Or, you might able to leverage this Perl interface to calling the W3 Validator on the web.
If you want to write a testing framework, I'd suggest taking a look at Test::More from CPAN as a good starting point. It's powerful but fairly easy to use and is definitely going to be better than cobbling something together as a one-off.
I'm trying to copy some files from one network share to another using File::Copy.
This is my code:
#!C:/strawberry/perl/bin/perl.exe
use File::Copy;
print "Content-type: text/html\n\n";
print "<H1>Hello World</H1>\n";
copy("s:\\nl\\cover\\config.jsp", "s:\\temp\\config.jsp")
or die "File cannot be copied.";
print "this is not displayed";
Why is the 'die' message not rendering?
If you are running this under a web server (I cannot imagine why, you are sending a "Content-Type" header), any error messages you emit using die and warn will go to the server's error log.
Further, if you are invoking this as CGI, note that you are lying to the browser by claiming you are sending HTML and not sending HTML.
Especially if you are just learning Perl, you should make an effort to dot all your is and cross all your ts:
#!C:/strawberry/perl/bin/perl.exe
use strict; # every time
use warnings; # every time
use CGI qw(:cgi);
use CGI::Carp qw(fatalsToBrowser); # only during debugging
use File::Copy;
use File::Spec::Functions qw(catfile);
$| = 1;
# prefer portable ways of dealing with filenames
# see http://search.cpan.org/perldoc/File::Spec
my $source = catfile(qw(S: n1 cover config.jsp));
my $target = catfile(qw(S: temp config.jsp));
print header('text/plain');
if ( copy $source => $target ) {
print "'$source' was copied to '$target'\n";
}
else {
print "'$source' was not copied to '$target'\n";
# you can use die if you want the error message to
# go to the error log and an "Internal Server Error"
# to be shown to the web site visitor.
# die "'$source' was not copied to '$target'\n";
}
See CGI for the function oriented interface import lists.
Are you sending your stderr to the stdout stream as well? All your prints will got to stdout which is presumably connected to a browser, given your HTML output.
However, die writes to the stderr stream. This is likely to go, not to the browser window, but to an error log of some sort. As to where it's going, it depends on what Perl is running within.
One way to check is to print something instead of dieing in the or clause.
So, some questions:
How are you running it?
If on the command line, show us the exact command.
If in a web server of some sort, tell us which one so we can find the logs for you.
die sends messages to STDERR, which will wind up in the web server's error logs, not on the screen. There are some CGI modules that offer you greater control over error-handling, or you could install a $SIG{__DIE__} handler (if you don't know what that is, then don't worry -- you don't need to), but when I want a quick-and-dirty way to debug my CGI scripts, I put this at the top of the script:
#! /usr/bin/perl
$src = join'',<DATA>;
eval $src;
print "Content-type: text/plain\n\n$#\n" if $#;
__END__
... my cgi script starts here ...
This loads the script into a variable, uses eval to run the Perl interpreter on that variable's contents, and prints any errors to standard output (the browser window) with a valid header.
copy("s:\\nl\\cover\\config.jsp", "s:\\temp\\config.jsp")
or die "File cannot be copied.";
print "this is not displayed";
Only one of these messages should ever be displayed and it's unclear which you're asking about.
The question says you're wondering why the die message isn't being displayed; to me, that implies that you're not seeing the message "File cannot be copied." and the most obvious reason for this is that the copy operation is succeeding, but see also the previous responses about looking in the error log if you're running this under CGI.
The text of the messages, though, suggests that you actually mean you're not seeing the message "this is not displayed". (Why else would you mention that it isn't displayed?) In that case, the reason you're not seeing it is because die causes the program to exit. After the copy fails and the die executes, your program is dead. Terminated. It has shuffled off this mortal CPU and joined the stack eternal. It wouldn't print "this is not displayed" if you put four million volts through it. It is an ex-process.
After editing your code, it's apparent that your die is seen as a command and probably needs to be escaped. Note how it is rendered on Stack Overflow in blue (indicating that it is a keyword). Try switching to a synonym like "shutdown" instead.