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

I don’t mess with procmail much anymore, but maybe these will be useful to someone.

Split a mailbox into separate files for each message:

$ formail -s sh -c 'cat - > foo.$FILENO' < klez.file

Resend a mailbox (foo) through a set of filters (rc.test):

$ formail -s procmail ./rc.test < foo

Move the last 10 messages from folder foo and put them in folder bar:

$ MSGS=`egrep '^From ' foo | wc -l`
$ formail +`expr $MSGS - 10` -s < foo > bar

Check which recipes triggered most often (based on a verbose log format):

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.

I don’t use emacs’ artist mode often enough to remember all of the keystrokes and finding the reference sometimes is effort than it’s worth.

To enable:

M-x artist-mode

to disable:

C-cC-c

Here is the list of commands from the artist.el file:

C-cC-aC-r  artist-toggle-rubber-banding
C-cC-al    artist-select-op-line
C-cC-aL    artist-select-op-straight-line
C-cC-ar    artist-select-op-rectangle
C-cC-aR    artist-select-op-square
C-cC-as    artist-select-op-square
C-cC-ap    artist-select-op-poly-line
C-cC-aP    artist-select-op-straight-poly-line
C-cC-ae    artist-select-op-ellipse
C-cC-ac    artist-select-op-circle
C-cC-at    artist-select-op-text-see-thru
C-cC-aT    artist-select-op-text-overwrite
C-cC-aS    artist-select-op-spray-can
C-cC-az    artist-select-op-spray-set-size
C-cC-aC-d  artist-select-op-erase-char
C-cC-aE    artist-select-op-erase-rectangle
C-cC-av    artist-select-op-vaporize-line
C-cC-aV    artist-select-op-vaporize-lines
C-cC-aC-k  artist-select-op-cut-rectangle
C-cC-aM-w  artist-select-op-copy-rectangle
C-cC-aC-y  artist-select-op-paste
C-cC-af    artist-select-op-flood-fill

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.