读书笔记--每天一个shell--06

这个shell是来判断输入的数字是否为合理的浮点数

The Code

#!/bin/sh

# validfloat -- Tests whether a number is a valid floating-point value.
# Note that this script cannot accept scientific (1.304e5) notation.

# To test whether an entered value is a valid floating-point number, we
# need to split the value at the decimal point. We then test the first part
# to see if it's a valid integer, then test the second part to see if it's a
# valid >=0 integer, so -30.5 is valid, but -30.-8 isn't.

. validint   # Bourne shell notation to source the validint function

validfloat()
{
  fvalue="$1"

  if [ ! -z $(echo $fvalue | sed 's/[^.]//g') ] ; then

    decimalPart="$(echo $fvalue | cut -d. -f1)"
    fractionalPart="$(echo $fvalue | cut -d. -f2)"

    if [ ! -z $decimalPart ] ; then
      if ! validint "$decimalPart" "" "" ; then
        return 1
      fi
    fi

    if [ "${fractionalPart%${fractionalPart#?}}" = "-" ] ; then
      echo "Invalid floating-point number: '-' not allowed \
        after decimal point" >&2
      return 1
    fi
    if [ "$fractionalPart" != "" ] ; then
      if ! validint "$fractionalPart" "0" "" ; then
        return 1
      fi
    fi

    if [ "$decimalPart" = "-" -o -z "$decimalPart" ] ; then
      if [ -z $fractionalPart ] ; then
        echo "Invalid floating-point format." >&2 ; return 1
      fi
    fi

  else
    if [ "$fvalue" = "-" ] ; then
      echo "Invalid floating-point format." >&2 ; return 1
    fi

    if ! validint "$fvalue" "" "" ; then
      return 1
    fi
  fi

  return 0
}

notice：

1）： if [ ! -z $(echo $fvalue | sed 's/[^.]//g') ] 将输入，以.分成整数和小数部分。

2）：if [ "${fractionalPart%${fractionalPart#?}}" = "-" ]  判断小数点后面如果接‘-’号，这输出字符不合法

3）接着的一些if语句就是判断小数及整数部分合不合法

4）由于 valiint函数没给出，脚本不能完全执行，valiint函数是判断字符串是否全为数字.