Specifications

So, the line ends up as follows:
sed -n ${pickline}p
That does the trick, and in an appli-
cation like this, sed is lightning fast too.
At this point, we have a data file of
interesting information, we can extract
a random line from the file, and we can
split the resultant data into the film title
and release year. How about coming up
with plausible alternative release years?
Calculating Random Years
My first inclination with generating ran-
dom years was to add and subtract 1–3
years and then use those as the alternate
values. If we were looking at, say, Shaun
of the Dead, released in 2004, we might
end up with 2001 and 2007 as the
options. Match a film that’s more recent
though, such as 2007’s Grindhouse
(though why that’s on the IMDb top 250
films list is beyond me), and we have a
problem. Suggesting 2009 as a possible
release date would be daft.
More important, it wouldn’t take
long for people to realize that it’s the
middle value that’s always correct on
the quiz—not good. Just like with the
SAT and GMAT, it’s important to avoid
any possible patterns in answers.
As a result, we can try something
a bit more complicated. Each possible
year is the actual year of release plus
or minus a random value of 1–5—close
enough that it’ll be challenging to
remember the right year.
Here’s the beginning of the script:
add="$(( $RANDOM % 2 ))"
delta="$(expr $(( $RANDOM % 5 )) + 1)"
Here, add will be 0 (false) or 1
(true) for later conditional testing,
and delta is a value between one and
five, just as we need. They can be
applied as follows:
if [ $add -eq 1 ] ; then
newvalue=$(expr $1 + $delta )
else
newvalue=$(expr $1 - $delta )
fi
This script can be tested easily by
dropping it into a simple script, which
I’ll call random-years.sh. The result of
applying this to the starting year 2000 is
2002, 1998, 2005, 2001, 2003, 2004.
Seems sufficiently random, yes?
Now, let’s consider some nuances.
First, we need to ensure that it’s never
past the current year, which can be
done by grabbing that value from the
date command with a format string:
date +%Y (learn more about the many,
many format strings that the date com-
mand understands with
man strftime ).
Second, here’s a more interesting
thought. If the movie came out a long
time ago, we should have a bigger delta
than if it’s a recent release. In other
words, if the movie is Casablanca, it
came out in 1942, 66 years ago. Iron
Man, which is also on the top 250 list,
came out in 2008, 0 years ago. For
Casablanca, we could have possible val-
ues of 1938 and even 1951, and it’d be
a good quiz question for anyone who
isn’t a complete film nut. But, that far
of a spread for Iron Man makes no
sense. No one’s going to think it might
have come out in 1999.
What I’m thinking about in this situa-
tion then is that the delta might be a
percentage of the age of the movie,
normalized so that we always have some
sort of spread. Maybe 20%? That’d give
us a delta of 13.2 for Casablanca and 0
for Iron Man. That could work.
Ah, but I’ve run out of space. Next
month, we’ll go back to the random
adjacent year function to wrap it up,
and then look at how to get these
questions out on Twitter rather than just
on the Linux command line. Until then,
“here’s lookin’ at you, kid.”
I
Dave Taylor is a 26-year veteran of UNIX, creator of The Elm Mail
System, and most recently author of both the best-selling Wicked
Cool Shell Scripts and Teach Yourself Unix in 24 Hours , among his
16 technical books. His main Web site is at www.intuitive.com,
and he also offers up tech support at AskDaveTaylor.com. Follow
him on Twitter if you’d like: twitter.com/DaveTaylor.
Just like with the SAT and GMAT, it’s important
to avoid any possible patterns in answers.