[SOLVED] Random float numbers in BASH

pharaoh19 · 03-27-2011, 04:43 PM

Hi people

I'm learning shell scripting using bash and I want to generate 4 floating point number with 5 decimal places and write them to a file and a variable. I've done all this except the $RAMDOM enviroment variable does not generate a float number but a integrer.

I hope you could explain why to lead me to a solution.
Thnak you all in advance.

PS: script so far

Code:

#!/bin/bash

#: Title		: randomFloats
#: Date			: 2011-03-27
#: Author		: pharaoh
#: Version		: 1.0 
#: Discription	        : Generate a 4 float numbers with 5 decimal places and write them to a file and a variable 


listFloats=0.0
for i in $(seq 0 3)
do
    aux=$[($RANDOM % 15000)]
	printf -v aux "%.5f" ${aux}
	
	#In the first iteration it just set the variable, in the others it append
	if [ $i -eq 0 ]
	then
		listFloats=${aux}
		printf ${aux} > randomFloats.txt
	else 
		listFloats="${listFloats} ${aux}"
		printf ${aux} >> randomFloats.txt
	fi
done

printf "%s\n" ${listFloats}

Nominal Animal · 03-27-2011, 05:12 PM

Note that $RANDOM range is [0, 32767] (not enough for five digits), and Bash does not have any support for floating-point arithmetic. You'll need to use fixed-point arithmetic or string manipulation, if you really want to do this with Bash.

A random number [0.00000, 1.00000):

Code:

v=$[(100 + (RANDOM % 100)]$[1000 + (RANDOM % 1000)]
v=0.${v:1:2}${v:4:3}
echo $v

Or, [0.00000, 15.00000):

Code:

v=$[100 + (RANDOM % 100)]$[1000 + (RANDOM % 1000)]
v=$[RANDOM % 15].${v:1:2}${v:4:3}
echo $v

Rather than Bash, I'd use e.g. awk for floating-point calculation and simple data manipulation:

Code:

awk 'BEGIN { printf("%.5f\n", rand() * 15.0) }'

although awk's rand() needs a seed via srand(), e.g.

Code:

awk -v "seed=$[(RANDOM & 32767) + 32768 * (RANDOM & 32767)]" \
       'BEGIN { srand(seed); printf("%.5f\n", rand() * 15.0) }'

kurumi · 03-27-2011, 07:26 PM

I recommend not using shell. Either one of the big P's or R (Python|Perl|PHP|Ruby) will do this easily for you

Ruby1.9+ (for random floats from 0 to 5)

Code:

$ ruby -e '1.upto(5){print "%.5f\n" % (rand * 5 + 0.0) }'
3.27893
2.63196
3.81157
0.46412
2.72308

dive · 03-27-2011, 07:43 PM

You could also use bc:

MULTIPLIER=10 # generates from 0 - 9.99999
echo "scale=5; $RANDOM*$MULTIPLIER/32767" | bc

pharaoh19 · 03-28-2011, 08:48 AM

Thank you guys!