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# 1  
Old 11-13-2002
Random Line

I am trying to build a script written in ksh93 that pulls a random line out of each of four text files.

Since the files are all different, I can't think of a way to take the number of lines (in one case, let's say 50), then randomly pick a line out, making sure that all lines have a fair chance...

I tried playing with some variations of division and comparison of the $RANDOM variable, but I was unsuccessful in making sure I didn't pick the same few lines over and over...

Any suggestions?
# 2  
Old 11-13-2002
try something like:

VAR=`expr $RANDOM % 50`
# 3  
Old 11-13-2002
I'll give that a shot!
I tried using division, but not using % (I can't remember what it's called ATM...). It appears that I get a good mix out of it!

Thanks crashnburn - I'll post my script if it turns out how I want it (i.e. - I don't abandon it first Smilie ...)

Last edited by LivinFree; 11-13-2002 at 07:14 PM..
# 4  
Old 11-14-2002
Suppose that you want to pick a random line froma file that has exactly 100 lines. You can label the lines 0 through 99. Then if you get a random integer, you just take the last two digits as your line number.

Those last 2 digits are the remainder that your get when you divide the random integer by 100. So for example, if the random integer is 10726352; you would have a remainder of 52 after dividing 10726352 by 100. This is expressed as
10726352 % 100 = 52
and % is sometimes called "the remainder function". And sometimes "modulus".

But is was important to divide by 100 since we had 100 lines in our file. When we divide by 100, we have 100 possible remainders, so each line in the file has a chance.

To make this general, don't divide by 100 (or 50) all the time, divide by the count of items.
# 5  
Old 11-14-2002
Thanks to Perderabo and Crashburn for this idea...

Code:
nlines=`wc -l filename`
VAR=`expr $RANDOM % $nlines + 1`

we need to add 1 so that we genrate line numbers between 1 to $nlines and not 0 to $nlines -1

or this should also work... here I'm ensuring by dividing with 32768 that the "random" number generated will fall within the no of lines that file contains.

On hp-ux 10, 11 we have man ksh giving

0 <= $RANDOM <= 32767

Code:
nlines=`wc -l filename`
VAR=`expr \( 1 + $RANDOM \) \* $nlines / 32768`

you can see the range for RANDOM by referring "man ksh" for your implementation...

Cheers!
Vishnu.

Last edited by Vishnu; 11-14-2002 at 12:37 PM..
# 6  
Old 11-14-2002
assuming a file size of 5 lines execute both these loops on your machine... you need to type CTRL+C to break the loops when you want...

Quote:
while [ 1 -gt 0 ]; do
expr $RANDOM % 5 + 1
done > newfile
Quote:
while [ 1 -gt 0 ]; do
expr \( 1 + $RANDOM \) \* 5 / 32768
done > newfile2
you will notice that newfile2 for most of the time won't contain 5... so the second way won't lead to a uniform distribution between 1 and $nlines... in fact most of the time it won't generate $nline at least for small $nline values...
# 7  
Old 11-20-2002
Well, I used the basic suggestions above, and came up with this fun little waste of time (in a post below - I couldn't attach the file, even though it's only 12k)

A little background - this is based on the BOfH Excuse Calendar. If you don't know who / what that is, read over here first:
http://bofh.ntk.net/Bastard.html

It's stored in shar format, created by GNU shar.

the "excuse" script assumes you have a working "/bin/ksh", and have common utilities like sed in your PATH.
excuse.web will output a weak excuse for HTML, and is meant to be called from serve_exc. serve_exc assumes that you have netcat (nc), and it's in your PATH, and it was compiled with GAPING_SECURITY_HOLE defined (to allow it to use the "-l" option)... It'll listen on port 8080 for a connection from a web browser, run excuse.web, then start over...

It may take some fiddling, but take the code below, put it in a file called excuse.txt, and type "sh excuse.txt". Then "./excuse" and repeat for endless hours of fun!

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