I gave a talk about Perl dependency isolation at Salt Lake Perl Mongers.

Some notes for using Devel::Cover.

Gathering coverage

CPAN::Reporter doesn’t have a build step, so we prove -l; we also don’t want to cover the world, so we set -inc=lib:

HARNESS_PERL_SWITCHES=-MDevel::Cover=-inc=lib prove -l

or:

PERL5OPT=-MDevel::Cover prove t/some-test.t

This will run the prove utility and turn on code coverage.

Selecting only one file to cover

cover -select=lib/Some/Module.pm

You may add multiple -select options.

Ignoring files to cover

cover -ignore_re=^/var/core_lib -ignore=/usr/bin/prove

I needed to come up with a way to spread out chunks of a subnet among a handful of users, so I came up with this routine:

sub hash256 {
    my $str  = shift;
    my $hmac = hmac_sha256($str);
    my $val  = unpack "L*" => $hmac;
    my $hash = $val % 256;

    return $hash;
}

Used:

for my $str ( qw/scott paul mark jayce rvd james/ ) {
    say sprintf "%-15s %d" => $str, hash256($str);
}

Now the result of my $hash = hash256('joe') can be used as, say, the third octet in a cidr: 192.168.$hash.0/24.

I gave a talk about functional programming with Perl at Salt Lake Perl Mongers.

I gave a talk about asynchronous programming patterns in Perl at Salt Lake Perl Mongers. This presentation ultimately landed me a new job—thank you to SLC.pm!

Here are some Perl goodies I forget to write down once I’ve remembered them long enough to solve my problem.

Line range

If you want to print all the lines in a file after a certain line number:

perl -ne 'print if (2655641 .. -1)' some.log

This will print from line 2655641 to the last line (-1).

Omiting chunks

Sometimes you have chunks of lines, or multi-line records, that you want to skip.

DBD::mysql knows that certain MySQL column types are integers with this call:

$sth->execute;
$nums = $sth->{'mysql_is_num'} || [];

You can iterate over $nums and see which columns are numeric-type columns. However, when you pull the data out, it’s converted to a string. So, what used to be as simple as this:

my $accounts = $sth->fetchall_arrayref({});

now requires this kind of trickery:

my @accounts = ();
my $is_num   = $sth->{'mysql_is_num'} || [];
while (my $row = $sth->fetchrow_arrayref) {
    push @accounts, {
        map {
            $Acct_Fields[$_] =>   ## key
              ($is_num->[$_]      ## check to see if it's int
                ? 0 + $row->[$_]  ## coerce to integer/numeric
                : $row->[$_])     ## leave it alone
        } (0 .. $#Acct_Fields)    ## number of keys
    };
}

This seems to work as a primary test to see if a scalar ($val) is an number-ish thing:

Here’s a nice trick from perlfunc’s map entry:

To force an anon hash constructor use "+{":

    @hashes = map +{ lc($_) => 1 }, @array # EXPR, so needs
                                           # comma at end

to get a list of anonymous hashes each with only one entry apiece.

Say you have a hash:

my %hash = (foo => 'fooey',
            bar => 'barey',
            baz => 'bazey',
            blech => 'blechey');

and you want to rename some of the hash keys, create another hash that holds the new names of the keys:

## old-name => new-name
my %new = (foo => 'foooo',
           bar => 'baaar');

Then this is a fast way to rename the keys. Measured on 2.4Ghz i5 MacBook Pro.

To selectively profile during only a portion of the code, invoke like this:

$ NYTPROF=start=no perl -d:NYTProf t/load.t -v

Then inside t/load.t add the following directives which tell Devel::NYTProf to start and stop profiling:

DB::enable_profile();
... ## profile this section
DB::finish_profile();

Add use Devel::NYTProf; in either the test file or in the module.