With the shell script, I wish to generate five files, and I wish to put different random number range from 50000~150000 in each file. I tried something like following,
for i in 01 02 03 04 05; do
A=$((50000+100000))
B=$(($B%$A))
cat > ${i}.dat << EOF
AArandom=$A
EOF
done
But this does not work.... How can I make random numbers and print out for each file?
Each time you read the value of the variable $RANDOM,
it gives you a random number between 0 and 2^15 - 1,
that is 0 and 32767. So that doesn't give you enough range.
You could use two $RANDOM as two digits of base-15,
and then take appropriate modulo and apply appropriate range normalization.
Here's the logic wrapped in a function:
randrange() {
min=$1
max=$2
((range = max - min))
((maxrand = 2**30))
((limit = maxrand - maxrand % range))
while true; do
((r = RANDOM * 2**15 + RANDOM))
((r < limit)) && break
done
((num = min + r % range))
echo $num
}
And then you can generate the files in a loop like this:
for i in 01 02 03 04 05; do
echo "AArandom=$(randrange 50000 150000)" > $i.dat
done
Note that there is a caveat in the implementation of randrange:
there is a loop to re-roll in case the value would be biased,
but theoretically this may prevent the function from terminating.
In practice, that's extremely unlikely, but deserves a mention.
RANDOM numbers resulting in each output number greater than 1, and two combinations resulting in 1 (one random number equal 0 and the other 1, or both numbers equal 2^15-1), making a result of 1 twice as likely as any other number.
shuf is probably what you want:
$ shuf -i 50000-150000 -n 1
148495
$RANDOMproduces numbers in the range0 - 32767, but here a bigger range is required.man bashis often a good way to start. The man page is long; search for keywords, likerandom...$Bwasn't used to output anything.