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#!/bin/bash
# primes2.sh
# Generating prime numbers the quick-and-easy way,
#+ without resorting to fancy algorithms.
CEILING=10000 # 1 to 10000
PRIME=0
E_NOTPRIME=
is_prime ()
{
local factors
factors=( $(factor $1) ) # Load output of `factor` into array.
if [ -z "${factors[2]}" ]
# Third element of "factors" array:
#+ ${factors[2]} is 2nd factor of argument.
# If it is blank, then there is no 2nd factor,
#+ and the argument is therefore prime.
then
return $PRIME # 0
else
return $E_NOTPRIME # null
fi
}
echo
for n in $(seq $CEILING)
do
if is_prime $n
then
printf %5d $n
fi # ^ Five positions per number suffices.
done # For a higher $CEILING, adjust upward, as necessary.
echo
exit
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