返回顶部

收藏

二进制到十进制的转换

更多

脚本 b2d 将二进制数 (比如 1101) 转换为相应的十进制数。这也是一个用expr命令进行数学运算的例子:

该脚本使用的算法是利用十进制和二进制数权值 (1,2,4,8,16,..),比如二进制"10"可以这样转换成十进制:

0 * 1 + 1 * 2 = 2

为了得到单个的二进制数我们是用了lastchar 函数。该函数使用wc ?c计算字符个数,然后使用cut命令取出末尾一个字符。Chop函数的功能则是移除最后一个字符。

#!/bin/sh
# vim: set sw=4 ts=4 et:
help()
{
 cat < b2h -- convert binary to decimal

USAGE: b2h [-h] binarynum

OPTIONS: -h help text

EXAMPLE: b2h 111010
will return 58
HELP
 exit 0
}

error()
{
  # print an error and exit
  echo "$1"
  exit 1
}

lastchar()
{
  # return the last character of a string in $rval
  if [ -z "$1" ]; then
    # empty string
    rval=""
    return
  fi
  # wc puts some space behind the output this is why we need sed:
  numofchar=`echo -n "$1" | wc -c | sed 's/ //g' `
  # now cut out the last char
  rval=`echo -n "$1" | cut -b $numofchar`
}

chop()
{
  # remove the last character in string and return it in $rval
  if [ -z "$1" ]; then
    # empty string
    rval=""
    return
  fi
  # wc puts some space behind the output this is why we need sed:
  numofchar=`echo -n "$1" | wc -c | sed 's/ //g' `
  if [ "$numofchar" = "1" ]; then
    # only one char in string
    rval=""
    return
  fi
  numofcharminus1=`expr $numofchar "-" 1`
  # now cut all but the last char:
  rval=`echo -n "$1" | cut -b 0-${numofcharminus1}`
}

while [ -n "$1" ]; do
case $1 in
  -h) help;shift 1;; # function help is called
  --) shift;break;; # end of options
  -*) error "error: no such option $1. -h for help";;
  *) break;;
esac
done

# The main program
sum=0
weight=1
# one arg must be given:
[ -z "$1" ] && help
binnum="$1"
binnumorig="$1"

while [ -n "$binnum" ]; do
  lastchar "$binnum"
  if [ "$rval" = "1" ]; then
    sum=`expr "$weight" "+" "$sum"`
  fi
  # remove the last position in $binnum
  chop "$binnum"
  binnum="$rval"
  weight=`expr "$weight" "*" 2`
done

echo "binary $binnumorig is decimal $sum"
#
#该片段来自于http://outofmemory.cn

标签:shell,基础

收藏

0人收藏

支持

0

反对

0

发表评论