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    <p>For reference, here are something resembling the "usual" ideal answers to this.</p> <pre><code>#!/usr/bin/env bash # Bash/ksh93 # Theoretically also zsh/mksh, but both have bugs that break it. function fib1 { # It is critical to validate user input if it will be used in an arithmetic # expression. [[ $1 == +([[:digit:]]) ]] || return 1 # Demonstrates an accumulating version to print the intermediary results. typeset i=1 f=(0 1) while (( i &lt; $1 )); do # Don't use expr(1) unless you're coding for Bourne. (( f[i] = f[i-1] + f[i++] )) done echo "${f[@]}" } fib1 "$1" </code></pre> <p>It is confusing that in addition to the broken syntax, you're using strange <code>expr</code> even with a <code>/bin/bash</code> shebang. You should read the bash manual and not read whatever suggested that to you.</p> <pre><code>#!/bin/sh # POSIX (posh/bash/zsh/all kshes) # It's easier to write a let wrapper than re-type test expressions repeatedly. # This emulates let precisely, but it's not important to understand everything # going on here. Breaks in dash because of its lack of support for the # otherwise ubiquitously supported comma operator, and busybox because of a bug in # its environment assignments. let() { IFS=, command eval test '$(($*))' -ne 0 } fib2() { # Uglier validation for POSIX case $1 in *[^[:digit:]]*|'') return 1 esac # Using globals for simplicity count=$1 n1=0 n2=1 while let count-=1; do let n1=n2 n2=${n1}+n2 done printf 'Fib Num: %d\n' "$n2" } fib2 "$1" </code></pre> <p>My arithmetic fibonacci is somewhat popular as a curiosity.</p> <pre><code># Bash/ksh93/zsh # Could be more elegant but includes bug workarounds for ksh/zsh $ a=a[++n%20]=a[n]+a[n-1],a[0] a[n=2]=1; let a a=0; echo "${a[@]}" 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 # Less portable because of bugs. Works in Bash. $ a=('a[a[n]=a[n-1]+a[n-2],n++/20]' 2 0 1); echo "${a[@]:n=4,a}" 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 </code></pre>
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    1. POCan someone tell me why this bash script won't run?
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    1. USormaaj
    1. USormaaj
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    1. COThanks for this. It's probably a bit much for a "complete beginner," yet a very worthwhile study. Nice use of `((` and `))`; and the validation is a great idea. Wish I could vote this up more.
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      1. USDave Jarvis
 

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