Home » Generate random numbers in specific range

# Generate random numbers in specific range

## Solutons:

You can try `shuf` from GNU coreutils:

``````shuf -i 1-100 -n 1
``````

In the POSIX toolchest, you can use `awk`:

``````awk -v min=5 -v max=10 'BEGIN{srand(); print int(min+rand()*(max-min+1))}'
``````

Do not use that as a source to generate passwords or secret data for instance, as with most `awk` implementations, the number can easily be guessed based on the time that command was run.

With many `awk` implementations, that command run twice within the same second will generally give you the same output.

# jot

On BSD and OSX you can use jot to return a single random (`-r`) number from the interval `min` to `max`, inclusive.

``````\$ min=5
\$ max=10
\$ jot -r 1 \$min \$max
``````

## Distribution problem

Unfortunately, the range and distribution of randomly generated numbers is influenced by the fact that jot uses double precision floating point arithmetic internally and printf(3) for output format, which causes rounding and truncation issues. Therefore, the interval’s `min` and `max` are generated less frequently as demonstrated:

``````\$ jot -r 100000 5 10 | sort -n | uniq -c
9918  5
20176 6
20006 7
20083 8
19879 9
9938  10
``````

On OS X 10.11 (El Capitan) this appears to have been fixed:

``````\$ jot -r 100000 5 10 | sort -n | uniq -c
16692 5
16550 6
16856 7
16579 8
16714 9
16609 10
``````

and…

``````\$ jot -r 1000000 1 10 | sort -n | uniq -c
100430 1
99965 2
99982 3
99796 4
100444 5
99853 6
99835 7
100397 8
99588 9
99710 10
``````

## Solving the distribution problem

For older versions of OS X, fortunately there are several workarounds. One is to use printf(3) integer conversion. The only caveat is that the interval maximum now becomes `max+1`. By using integer formatting, we get fair distribution across the entire interval:

``````\$ jot -w %i -r 100000 5 11 | sort -n | uniq -c
16756 5
16571 6
16744 7
16605 8
16683 9
16641 10
``````

## The perfect solution

Finally, to get a fair roll of the dice using the workaround, we have:

``````\$ min=5
\$ max_plus1=11  # 10 + 1
\$ jot -w %i -r 1 \$min \$max_plus1
``````

## Extra homework

See jot(1) for the gory math and formatting details and many more examples.

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