Bash script which generates n elements of the Fibonacci sequence, iteratively

fib_iter.sh

#!/bin/bash

# source https://en.wikipedia.org/wiki/Fibonacci_number
# assuming F_1 = 1 and F_2 = 1 for seed values

read -p "Enter Count of Fibonacci Terms: " F_count

# input checking
re='^[0-9]+$'
if ! [[ $F_count =~ $re ]] ; then
       echo "Not a valid integer, exiting..." >&2; exit 1
fi

# begin script
F_1=1
F_2=1
F_n=0 # initial value of seq number

# subtract 2 from number of terms to deal with
# special case of seed terms
F_count=$(($F_count-2))

echo -n "$F_1 "
echo -n "$F_2 "

for i in `seq $F_1 $F_2 $F_count`
do
    F_n=$(($F_1+$F_2))
    echo -n "$F_n "
    F_1=$F_2
    F_2=$F_n
done

# carriage return / line feed cleanup
echo