fibo.sh

Shall高级编程

#!/bin/bash
# fibo.sh : Fibonacci sequence (recursive)
# Author: M. Cooper
# License: GPL3

# ---------------------------------
# Fibo(0) = 0
# Fibo(1) = 1
# else
#   Fibo(j) = Fibo(j-1) + Fibo(j-2)
# ---------------------------------

MAXTERM=15       # Number of terms (+1) to generate.
MINIDX=2         # If idx is less than 2, then Fibo(idx) = idx.

Fibonacci ()
{
  idx=$1   # Doesn't need to be local. Why not?
  if [ "$idx" -lt "$MINIDX" ]
  then
    echo "$idx"  # First two terms are 0 1 ... see above.
  else
    (( --idx ))  # j-1
    term1=$( Fibonacci $idx )   #  Fibo(j-1)

    (( --idx ))  # j-2
    term2=$( Fibonacci $idx )   #  Fibo(j-2)

    echo $(( term1 + term2 ))
  fi
  #  An ugly, ugly kludge.
  #  The more elegant implementation of recursive fibo in C
  #+ is a straightforward translation of the algorithm in lines 7 - 10.
}

for i in $(seq 0 $MAXTERM)
do  # Calculate $MAXTERM+1 terms.
  FIBO=$(Fibonacci $i)
  echo -n "$FIBO "
done
# 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610
# Takes a while, doesn't it? Recursion in a script is slow.

echo

exit 0