Linux Shell编程if语句内判断参数(3)

  -z string               如果 string 长度为零,则为真               [ -z $myvar ]

  -n string                      如果 string 长度非零,则为真        [ -n $myvar ]

  string1 = string2         如果 string1 与 string2 相同,则为真     [ $myvar = one two three ]

  string1 != string2        如果 string1 与 string2 不同,则为真     [ $myvar != one two three ]

  算术比较运算符

  num1 -eq num2              等于         [ 3 -eq $mynum ]

  num1 -ne num2              不等于       [ 3 -ne $mynum ]

  num1 -lt num2               小于        [ 3 -lt $mynum ]

  num1 -le num2            小于或等于     [ 3 -le $mynum ]

  num1 -gt num2             大于          [ 3 -gt $mynum ]

  num1 -ge num2             大于或等于    [ 3 -ge $mynum ]

  脚本示例:

  #!/bin/bash

  # This script prints a message about your weight if you give it your

  # weight in kilos and hight in centimeters.

  if [ ! $# == 2 ]; then

  echo "Usage: $0 weight_in_kilos length_in_centimeters"

  exit

  fi

  weight="$1"

  height="$2"

  idealweight=$[$height - 110]

  if [ $weight -le $idealweight ] ; then

  echo "You should eat a bit more fat."

  else

  echo "You should eat a bit more fruit."

  fi

  # weight.sh 70 150

  You should eat a bit more fruit.

  # weight.sh 70 150 33

  Usage: ./weight.sh weight_in_kilos length_in_centimeters

  位置参数 $1, $2,..., $N,$#代表了命令行的参数数量, $0代表了脚本的名字,

  第一个参数代表$1,第二个参数代表$2,以此类推,参数数量的总数存在$#中,上面的例子显示了怎么改变脚本,如果参数少于或者多余2个来打印出一条消息。

  执行,并查看情况。

  # bash -x tijian.sh 60 170

  + weight=60

  + height=170

  + idealweight=60

  + '[' 60 -le 60 ']'

  + echo 'You should eat a bit more fat.'

  You should eat a bit more fat.

  其中-x用来检查脚本的执行情况。

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