Calculate the Fibonacci sequence using bash

Question

I would like your opinion on my shell script that prints the Fibonacci sequence.

#!/bin/bash
first=0
second=1
third=1
echo -n "Term: "
read term
fub=$((second+third))
echo $second
echo $third
echo $fub
for ((i=1; i<term; i++))
do
 third=$((fub+third))
 echo $third
 fub=$((third+fub))
 echo $fub
done

I tried to calculate the Fibonacci sequence in the simplest way (without the use of recursive functions).

• Wildcard: Just so you know, bash is extremely inefficient for this type of usage. If you want to change system settings, install software, or generally handle anything to do with files, use bash. For computational/algorithmic type problems, not so much. As someone (Xanthir) on the xkcd forums wrote, "The correct way to write anything in Bash is to write it in ANY OTHER LANGUAGE, then call it from a bash script." Which is crude but accurate for computational/algorithmic type problems.
• Bruce Blacklaws: Yeah, I understand that. BASH is not granular enough for specific mathematical logic.

Answer 1

What does "Term" mean? I'd prefer to see 5 numbers if the user entered 5.

#!/bin/bash
echo -n 'Term: '
read term
i=0
j=1
for (( c=0; c<term; c++ )) ; do
 (( n=i+j ))
 (( i=j ))
 (( j=n ))
 echo $i
done

• Mingye Wang: Looks like terminal, terminate or something like that. end then.

Answer 2

While I don't write in Bash, I do know that you don't need more than two variables, at the most, to compute the Fibonacci sequence. In fact, you're very close to doing so.

Just sort of manipulating your code here,

#!/bin/bash
# first was never used, it was not required
second=1 # Somewhat confusing name, consider something different
third=1 # Same here.
echo -n "Term: "
read -r term # Using the -r argument was recommended after research
# Notice this functions without the beginning section
for ((i=1; i<term; i++))
do
 echo $second
 second=$((second+third))
 echo $third
 third=$((second+third))
done

If you were to apply this code to your picture above, simply replace all instances of fub with second.

---

Edit:

The modified code should display 2*term-2 numbers, (Your code as it is now displays more, 2*term+1 numbers)

To change this so it only displays term numbers, change term so it's the proper upper limit after you've read it.

So, the code could look something like this:

for ((i=1; i<term/2+1; i++))

---

Tested it and yes, the code does work.