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.

Here are some notes I keep for myself when I play with iptables (I don’t use it often enough to remember how it works):

List all rules

# iptables -L

See the rules and their numbers

# service iptables status

Delete a rule

# iptables -D CHAIN NUM

E.g.:

# iptables -D INPUT 12

Add a new rule at the bottom of the chain

# iptables -A INPUT -i eth0 -p tcp --dport 8888 -j ACCEPT

Insert a new rule in a particular place

This inserts a rule in position 6; the rule that was formerly in 6th position will be bumped down (and all rules below it):