The Unix Programming Environment (1984): trying an example on Linux

Good old fashioned book learning

I don't know what happened to my original copies of the two books we use to use as Unix bibles: Kernighan and Ritchie's "The C Programming Language" and Kernighan and Pike's "The Unix Programming Environment". Lost in a house move maybe. We often talk of one mythical box that contains everything we can no longer find but disappeared during a move, and they are probably in that box.

I did buy a copy of "The Unix Programming Environment" from a local second hand bookstore some time ago, it's entertaining, informative and has a brief overview of everything from file system fun to C programming and troff. It even has a section on using the "ed" editor, which isn't installed by default on anything anymore (sudo apt-get install ed fixes that). Mostly I use it to refresh those shell scripting skills I used to have but have atrophied over years of using Windows. However it seems some of the bourne shell examples don't seem to work on Linux, not because bash isn't great, but because the linux executables sometimes don't behave like they used to 30 years ago. Today's example: date(1).

GNU date or BSD date

The first example in the shell programming chapter in the book has a small wrapper for "cal(1)" that allows you to type in a calendar month as a word, rather than the month number. It's a fine little example, using case statements, the "set" shell built-in, command line arguments etc. But if you type it in as described in the book, it doesn't work.

The problem is trivial, date(1) when run as is used to put the year as the 6th output, but the version on this machine (Debian 11) puts the year as the 4th output. It's probably a GNU date thing vs a BSD date thing. Fixing the script isn't hard (original found on page 135, chapter 5 of the 1984 edition of the book)

#!/bin/sh

# cal2: nicer interface to /usr/bin/cal

case $# in
0) set `date`; m=$2; y=$4 ;; # no args: use today
1) m=$1 set `date`; y=$4 ;; # 1 arg: use this year
2) m=$1; y=$2 ;;
esac

case $m in
jan*|Jan*) m=1 ;;
feb*|Feb*) m=2 ;;
mar*|Mar*) m=3 ;;
apr*|Apr*) m=4 ;;
may*|May*) m=5 ;;
jun*|Jun*) m=6 ;;
jul*|Jul*) m=7 ;;
aug*|Aug*) m=8 ;;
sep*|Sep*) m=9 ;;
oct*|Oct*) m=10 ;;
nov*|Nov*) m=11 ;;
dec*|Dec*) m=12 ;;
[1-9]|10|11|12) ;;  # numeric month
*)          y=$m; m="" ;; # plain year
esac

/usr/bin/cal $m $y                 # run the real one

(note - modified from the original that had "y=$6" as the means of grabbing the year from the date(1) command)

I don't mind this copy of the book is out of date or that Linux/GNU isn't really the BSD that Kernighan and Pike used, I think you learn more from having to fix a broken example anyway. If you come across a copy of this book, It's as useful today as it was when my first boss shoved it in my hands and sent me off to a vt220 hooked up to a Pyramid to start my first day on the job. Next job is to find a proper 1980s copy of the C book.

Popular posts from this blog

Tailscale ate my network (and I love it)

Image
No matter where you go, there you are If you're like me, you travel occasionally. Access to your office from home, or from an airport lounge, or from a hotel room is paramount to being productive for most of us now. While I had a fairly simple Tailscale setup that got me into my test machines in the office, what I really wanted was to integrate my AWS production VPC into that system. It's surprisingly simple. Tailscale AWS instructions What do you want to do that for? In the "before tailscale" times, if I needed to test against the production AWS resources or connect dBeaver for database maintenance, I would edit the security group to add my IP address, do my testing, edit the security group to remove myself. This is as error prone as it sounds. I quite often forgot to remove my IP address from the allowed addresses, a major potential security risk when you are travelling. Tailscale has an extremely nifty way to get around it: if you run up a small ec2 ins...
Read more

Stupid stunts with WSL2 , Python3 and AWS ECS

Image
Hand rolled CMS system gets a previewer The ongoing process of updating the help system on the SmartShepherd inspired two new features: editing of the html in a temporary location and a small web server to check your work before pushing it to production. The surprise? That GitHub desktop will show you a side-by-side view if you change an image file. Can't believe I didn't notice that before. Can you hold my camel for me? Sometimes I get so far down a dead end I don't realise how many issues could be sorted simply by re-thinking something. The initial deployment of the SmartShepherd web server was to an Elastic Beanstalk setup on AWS, mostly because I had no idea what I was doing. Elastic Beanstalk isn't really one product, it's more of an elaborate script that creates systems for you. In my case, it was spinning up a small Windows EC2 instance, installing the .NET Core website and auto-configuring a load balancer to point to that instance. I mean, it's...
Read more

Time machine: Solaris 2.6 on QEMU

Image
You can never go home A big chunk of my professional career in the 1990s was spent with a Sparcstation on my desk. Before that the 68000 Sun2 and Sun3 floated past my sticky fingers but the Sparc machines quickly superseded those. I don't remember too much about which ones: pretty sure there was at least one IPX, one Sparcstation 5, a Sparcstation 10 and then the last one was most likely an Ultra 1 or maybe even an Ultra 5. It was a long time ago. Every now and again I think about how productive those machines were and do a little Ebay digging on how much one would be worth to have around. Except I don't have the room for more machines and the idea of trying to revive 25 year old hardware from that era is well beyond my electronic capabilities. Never fear, QEMU is here. Following these excellent instructions from Adafruit , you too can install Solaris 2.6 and have your very own emulated machine. Note that there is one instruction in there I am not sure you need. A...
Read more