Redirect and Restore STDERR in Dancer

Question

When starting my http server I don't want to see >> Dancer2 v0.201000 server <pid> listening on http://0.0.0.0:<port> printed on the stderr. Thats why I added the following line before calling start()

get "/pwd" => sub {
    my $pwd = cwd;
    print STDERR "\n\n[PWD] : $pwd\n"; # this line is not being printed
    print "\n\n[STDOUT::PWD] : $pwd\n";
    my %responseHash = ( pwd => $pwd );
    my $response = encode_json \%responseHash;
    return $response;
};    

my $dancerStartErr;

sub startServer {
    open (local *STDERR, ">", \$dancerStartErr) 
        or die "Dup err to variable error: $!\n";

    start();
}

startServer();

The problem is that later I can't print something on the STERR. How can I reopen STDERR (open(STDERR, ">", \*STDERR); doesn't help)?

Do you want to disable all logging, or just the very first message? — simbabque, Sep 19 '16 at 15:17

simbabque · Accepted Answer · 2016-09-19T15:31:42.993

If you don't want your application to log anything, you can change the logging engine to use Dancer2::Logger::Null. You do that by editing your config.yml, or in one of your environments. For example, to turn it off in producion, change # appdir/environments/production.yml.

logger: 'null'

The default is the logging engine 'console', which prints stuff to your terminal.

There are other Dancer2::Logger:: classes available bundled with Dancer2 and on CPAN in their own distributions. A better solution to just dumping everything into a black hole might be to log to a file instead. Documentation of how to configure it further can be found in Dancer2::Core::Role::Logger.

Also note that instead of printing to STDERR in your code, you should use the logging keywords with the appropriate log level.

print STDERR "\n\n[PWD] : $pwd\n"; # this line is not being printed

This is not a good idea, because you cannot distinguish if this is an error, or a warning, or just debugging output. That's why there are different log levels built into Dancer2.

core
debug
info
warning
error

All of them are available as keywords. There is documentation on it in Dancer2::Manual.

Since the working directory is probably not relevant in production, but only during development, you'd go with debug.

debug "[PWD] : $pwd";

That's it. It takes care of newlines and such for you automatically.

score 0 · Answer 2 · answered Sep 19 '16 at 08:53

0

You could use select before redirecting to save it in a variable

my $oldfh = select(STDERR);

and then use it later

select($oldfh);

Also check out:

answered Sep 19 '16 at 08:53

Chankey Pathak

21,187
12
85
133

I added a global variable `$STDERR_COPY` and then tried to print to stderr with `my $stdErr = select($STDERR_COPY);` and then I try to print on the `stderr` I get `Can't use string ("main::STDERR") as a symbol ref while "strict refs" ` – bob_saginowski Sep 19 '16 at 13:12

Redirect and Restore STDERR in Dancer

2 Answers2