random letters

pixellany · 06-27-2007, 11:49 PM

I am playing with a script to generate random characters--ie UC or LC letters, numbers, etc.
After generating a random number (decimal), I use this statement to generate the character:

Code:

printf "\x$(printf "%x" $a)"

("a" is the decimal # already generated.)
This works perfectly--my question is" Is there a simpler way?

The best solution would be a direct way of generating random characters, but I have not seen such a thing.

j-ray · 06-28-2007, 05:21 AM

you could set an array of characters, then set a random number x within the range of 0 - number of array elements-1 and take the charArr[x] as random character.

pwc101 · 06-28-2007, 05:50 AM

If want gibberish, then cat /dev/urandom or cat /dev/random will give you that (urandom being pseudo random, whereas random is more or less truly random, but is finite without external input - e.g. mouse movement etc.). Use strings to turn it into something a bit more recognisable:

Code:

strings /dev/urandom 
or 
strings /dev/random

edit: to test this, might be worth piping it into less, otherwise your terminal will very quickly fill up with rubbish!

Guttorm · 06-28-2007, 06:59 AM

If it's passwords you want, why not use pwgen?

pixellany · 06-28-2007, 08:19 AM

Thanks to all.....

The array method came to me while going to sleep--that one is the obvious head-slapper.

With the strings method, I don't see the easy way of limiting to a range---ie all LC letters. Also when I did "strings /dev/random" it printed maybe ten characters and then stopped.

No "pwgen" on this machine---will have to try that.

Guttorm · 06-28-2007, 08:24 AM

pwgen should only be an apt-get away

pwc101 · 06-28-2007, 08:28 AM

Quote:

Originally Posted by pixellany

Also when I did "strings /dev/random" it printed maybe ten characters and then stopped.

If you do "strings /dev/random", and then wiggle the mouse for a few seconds, it will create new random characters. man urandom has this to say on it:

Quote:

Originally Posted by man urandom

The /dev/random interface returns random bytes
only when sufficient amount of entropy has been collected.
If there is no entropy to produce the requested number of
bytes, /dev/random blocks until more entropy can be
obtained.

...

Bytes retrieved from /dev/random provide the highest quality
random numbers produced by the generator, and can be used to
generate long term keys and other high value keying
material.

If you only want lowercase/uppercase/whatevercase, perhaps a pipe to tr is your friend?

pixellany · 06-28-2007, 08:55 AM

Quote:

Originally Posted by pwc101

If you do "strings /dev/random", and then wiggle the mouse for a few seconds, it will create new random characters. man urandom has this to say on it:If you only want lowercase/uppercase/whatevercase, perhaps a pipe to tr is your friend?

Strings seems to be a really slow way of getting random letters, numerals, etc.

For setting the range, I think throwing away certain characters would skew the statistics. To generate random numbers, I first generate from 0 to an upper limit by using modulo division. Then I add a constant to set the lower end. This--in principle--gives a gaussian centered in the middle of the final range. I don't think you would get a gaussian distribution by just discarding.

This is really turning into an exercise in programming techniques---there is actually not a big market for random letters....

bigearsbilly · 06-29-2007, 02:56 AM

perl -e 'print chr rand(127-32)+32 while 1'

Code:

@k$FX0wX#kM>:() gO1#gJpLdV8eWQRb5`r>
5=o]M34M71:i<a>1Iv|yxDw+?$\YnT1k
2fQjXzHN|z?}T"lXVT6D?sDsyN<Uk-~_kw
JUb0C&?R05>ur(MKm}HBrfj0V%>]<Ksf^'5Ll2H*
vW4A^+XKMOf~CvU&y\>*,Ve=MXc(pSR,r2C2w )z>n6&
+s;;{gpbrdB9(o8veUCX]Y]3fR S

archtoad6 · 07-11-2007, 12:53 PM

Yes, an interesting programming exercise.

What is the goal? -- passwords?

What are the language constraints? -- bash only, or is perl allowed?

archtoad6 · 07-11-2007, 04:36 PM

Definitely an interesting exercise in programming techniques.

What was the original goal? -- passwords?

What are the language constraints? -- bash only, or is perl allowed?

pixellany · 07-11-2007, 05:45 PM

I wanted to get some random text in bash--it then turned into various bits of minutiae on how bash stores and converts raw bytes.

(I don't do Perl---I am learning Python, but that's another story.)

bigearsbilly · 07-12-2007, 02:26 AM

Quote:

I don't do Perl

you should try it, it's good for messing about with bytes...

e.g a bit of binary...

Code:

$  perl -e 'print unpack "B*", "Hello"'
0100100001100101011011000110110001101111

$ perl -e 'print pack "B*", "0100100001100101011011000110110001101111"'
Hello

archtoad6 · 07-12-2007, 05:27 AM

In post #1, where were you getting the decimal random #?

If you adopted the array method in post #2, how would you map the random # onto the array index? And I mean specific bash code -- i.e. will built-in bash arithmetic suffice, or will you need bc or something like it?

BTW, I agree:

Quote:

throwing away certain characters would skew the statistics

pixellany · 07-12-2007, 08:04 AM

bash has a built-in function: $RANDOM

I have not used the array method, but I assume that you would simply do:
num=$RANDOM
char=array[$num]

To avoid just throwing things away that don't fit the range (LO to HI), I set an upper bound which is the difference between HI and LO, then add LO back to the random number