Share scripts, the same problem, PHP and Shell notation

About writing scripts, 1 2 3 5 8 13 ...... Write it out with a script, what's the 100th number?

Shell

######### #下面是脚本内容 ##########

#!/bin/bash
For ((i=1;i<=100;i++))
Do
If [$i-eq 1];then
Let S[1]=1
elif [$i-eq 2];then
Let s[2]=2
Else
Let s[$i]=s[i-1]+s[i-2]
Fi
Done
echo "$ ((s[100]))"

######### #shell脚本到此为止 # # # #

It is worth noting that let do mathematical operations without using $, the final output of the 100th number, to add (()), otherwise only output S[100]

Php

Here is the script content/////////////////

<?php
for ($i =1; $i <=100; $i + +)
{
if ($i ==1)
{
$s [1]=1;
}
ElseIf ($i ==2)
{
$s [2]=2;
}
Else
{
$s [$i]= $s [$i -1]+ $s [$i-2];
}
}
echo "$s [100]";
?>

The script ends here///////////////////

It is worth noting that if the judgment is = = or = = =, it is best to add the contents of each if statement {}.