ChickenProp

After installing Arch on my Raspberry Pi, internet worked out of the box: I could plug it into the router, turn it on, ssh in and start downloading things. But the router is in my housemate's bedroom, which isn't ideal. If I want the Pi to be connected to the internet in my room, I need it to be connected to my laptop. (Another option would be a USB wifi dongle, of course.) This is how I did it. Much credit goes to the Ubuntu wiki's Connection sharing page.

I should disclaim that I don't fully understand networking stuff, and some of what I say might be wrong. I also didn't write this as I was going; so while I've consulted my browser and shell histories, it's possible I've forgotten some steps.

My laptop is running Gentoo, and this is where most of the work has to be done. It connects to the internet through wifi, on interface wlan0. The ethernet port is eth0, and eth0 is also the name of the ethernet port on the Pi.

Step zero: plug ev

ChickenProp

My root filesystem is on an SD card, and when I got a Raspberry Pi I decided to swap that SD card for a larger one and use the original in the Pi. This post chronicles my attempts to copy the filesystem.

Day One

I only have one SD card slot, which means I need to copy through an intermediate storage device. I have a backup disk, so that's not a problem. I also need another operating system, since I can't use my normal one while copying things to the new SD card. (I also no longer have the original OS on my netbook, because I've been using that partition for swap space.) Years ago I put a copy of Ubuntu on a USB stick "in case of emergencies" (I think this is the first time I've needed it), so that's not a problem either.

The new SD card already has one full-size partition, so the first step is to install ext3 on it:

mkfs.ext3 /dev/sdd1

ChickenProp

The point of this post is an attempt to calculate e to given precision in bash, a challenge given in a job listing that I saw recently. I kind of got nerd sniped. I wrote this as I went along, so there may be inconsistencies.

###First attempt###

The obvious method to compute e is as the infinite sum of 1/n!, n from 0 to ∞. This converges quickly, but how far do we have to calculate to get the n'th digit of e? We can deal with that later.

We obviously need a factorial function.

fac() {

ChickenProp

Silly things to do with shebang lines

The recent post on Hacker News about #! semantics surprised me. I had always assumed that a shebang line like

#! /usr/bin/prog -a -b

Would be equivalent to calling

$ /usr/bin/prog -a -b <file>