Git has a nice feature called bisect that’s immensely useful for finding out where and when something broke.

For this example, we’ll use small integers for commit ids because they’re easier to reason about and orderly. In reality, they’ll be long SHA hashes.

Let’s say you have a commit history like this:

commit 12
Author: Joe

commit 11
Author: Scott

commit 10
Author: Scott

commit 9
Author: Scott

commit 8
Author: Miles

commit 7
Author: Joe

commit 6
Author: Dave

commit 5
Author: Bob

commit 4
Author: Joe

commit 3
Author: Dave

Pretend you’re Dave (your last commit was commit 6) and you do a git pull and an ‘install-dev’ and see that the site’s busted, CSS all over the place, whatever. Git bisect to the rescue. First, tell git you’re ready to have it help you find the problem:

I found a fast way to add a new column to a table.

MySQL

1. Create the new table like the old table (foo), but with the new column you want in it. Make the new table with a different name (foo_new):

2. Add the records from the old table into the new table:

    INSERT INTO foo_new (col1, col2, col3)
         SELECT col1, col2, col3 FROM foo
   

3. If you have a lot of records, you can disable index updates during insert:

I made these notes as a result of my experimentation with a Raspberry Pi. I kept messing up the software on the SD card and needed to start over, but it took a long time to go through all of the RPi setup steps. By copying the partitions, I was able to restore relatively quickly.

Get the info of each partition you want to copy on your SD card using diskutil:

This little program uses currying to create a nested function reference that prints out a table with all possible permutations of the @states array in as many columns as you like.

#!/usr/bin/env perl
use strict;
use warnings;
use feature 'say';

## Scott Wiersdorf
## Created: Sat Aug 18 14:29:03 MDT 2012

## permutation/truth table generator

my $inputs = shift @ARGV || 3;  ## table columns
my @states = ('T', 'F', '-');   ## possible states

my $func = sub { say join "\t" => @_ };
for (1..$inputs) {
    $func = loop_maker($func);
}
$func->();

exit;

sub loop_maker {
    my $inner = shift;

    return sub {
        for my $state ( @states ) {
            $inner->(@_, $state);
        }
    };
}

The output with an argument of ‘2’ looks like:

Some miscellaneous notes I may split out into separate posts later… don’t bookmark this one.

View open network connections on OS X

sudo lsof -lnP +M -i4

The options:

-l      don't convert uids to login
-n      dont' convert network numbers to to hostnames
-P      don't convert port numbers to service names
+M      enable portmapping
-i4     look for IPv4 connections

See also nettop. 3rd party apps include Little Snitch and RubberNet.

Here are a few notes I’ve made when using LaTeX:

Hyphens

For two literal hyphens, separate them with {}, for example:

The \texttt{-{}-delete} flag should be set.

Underscores

Underscores are special; escape them if you want to use them literally:

Check the \texttt{authorized\_keys} file.

Working with Perl’s references can sometimes be confusing. This document illustrates several ways to efficiently take a slice of a hash reference.

Here is a hash reference and an array of keys called @order:

my $row = { foo => 'bar',
            baz => 'blech',
            one => 'uno',
            tres => 'three',
            cuatro => 'four or so' };
my @order = qw(one tres cuatro baz foo);

Here is one way to get a list of values in the order of @order:

Some notes about git. As with all my technical posts, some or all of this may be out of date. Consider it, then, courage to believe that there may be a solution to your problem in terms you can understand.

I have a local repository I want to make into a remote repository

Here’s our local repository:

local $ git init .
local $ git add .
local $ git commit . -m "- initial commit"

Nice. Now make an empty repo on the remote server:

Some notes I kept when I was learning how to use yum.

Installing a package that has been excluded

The file /etc/yum.conf may contain an ’excludes’ line that will disallow updates of any of packages listed. To bypass this, you can comment out those packages in /etc/yum.conf, or you can one-off it like this:

yum --disableexcludes all install gcc

Finding which repo has the file you need

yum provides '*apxs*'

You may need to add ‘–disableexcludes all’ too.