Shell函数的7种用法介绍

1. 在shell文件内部定义函数并引用：

[~/shell/function]# cat factorial.sh 

#!/bin/bash

function factorial

{

factorial=1

for (( i=1;i <= $1;i++ ))

        do

        factorial=$[ $factorial * $i ]

        done

echo $1的阶乘是:$factorial

}

echo '程序名':$0,用于求阶乘

factorial $1

[~/shell/function]# ./factorial.sh 10

程序名:./factorial.sh,用于求阶乘
10的阶乘是:3628800

2.返回值

函数返回码是指函数最后一条命令的状态码,可以用于函数返回值
使用return命令手动指定返回值：

[~/shell/function]# cat return.sh 

#!/bin/bash

function fun1 {

  read -p "enter a: " a

  echo -n "print 2a: "

  return $[ $a * 2 ]

}

fun1

echo "return value $?"

[~/shell/function]# ./return.sh 

enter a: 100

print 2a: return value 200

由于shell状态码最大是255，所以当返回值大于255时会出错。

[~/shell/function]# ./return.sh 

enter a: 200

print 2a: return value 144

3.函数输出

为了返回大于255的数、浮点数和字符串值，最好用函数输出到变量：

[~/shell/function]# cat ./fun_out.sh 

#!/bin/bash

function fun2 {

  read -p "enter a: " a

  echo -n "print 2a: "

  echo $[ $a * 2 ]

}

result=`fun2`

echo "return value $result"

[~/shell/function]# ./fun_out.sh     

enter a: 400

return value print 2a: 800

4.向函数传递参数(使用位置参数)：

[~/shell/function]# cat ./parameter.sh 

#!/bin/bash

if [ $# -ne 3 ]

then

    echo "usage: $0 a b c"

    exit

fi

fun3() {

    echo $[ $1 * $2 * $3 ]

}

result=`fun3 $1 $2 $3`

echo the result is $result

[~/shell/function]# ./parameter.sh  1 2 3

the result is 6

[~/shell/function]# ./parameter.sh  1 2

usage: ./parameter.sh a b c

5.全局变量与局部变量

默认条件下，在函数和shell主体中建立的变量都是全局变量，可以相互引用，当shell主体部分与函数部分拥有名字相同的变量时，可能会相互影响，例如:

[~/shell/function]# cat ./variable.sh    

#!/bin/bash

if [ $# -ne 3 ]

then

    echo "usage: $0 a b c"

    exit

fi

temp=5

value=6

echo temp is: $temp

echo value is: $value

fun3() {

    temp=`echo "scale=3;$1*$2*$3" | bc -ql`   

    result=$temp

}

fun3 $1 $2 $3

echo "the result is $result"

if [ `echo "$temp > $value" | bc -ql` -ne 0 ]

then 

    echo "temp is larger"

else

    echo "temp is still smaller"

fi

[~/shell/function]# ./variable.sh  12 3 2

temp is: 5

value is: 6

the result is 72

temp is larger

在这种情况下，在函数内部最好使用局部变量，消除影响。

[~/shell/function]# cat ./variable.sh 

#!/bin/bash

if [ $# -ne 3 ]

then

    echo "usage: $0 a b c"

    exit

fi

temp=5

value=6

echo temp is: $temp

echo value is: $value

fun3() {

    local temp=`echo "scale=3;$1*$2*$3" | bc -ql`   

    result=$temp

}

fun3 $1 $2 $3

echo "the result is $result"

if [ `echo "$temp > $value" | bc -ql` -ne 0 ]

then 

    echo "temp is larger"

else

    echo "temp is still smaller"

fi

[~/shell/function]# ./variable.sh  12 3 2

temp is: 5

value is: 6

the result is 72

temp is still smaller

6.向函数传递数组变量：

[~/shell/function]# cat array.sh 

#!/bin/bash

a=(11 12 13 14 15)

echo ${a[*]}

function array(){

  echo parameters : "$@" 

  local factorial=1

  for value in "$@"

  do

    factorial=$[ $factorial * $value ]

  done

  echo $factorial

}

array ${a[*]}

[~/shell/function]# ./array.sh 

11 12 13 14 15

parameters : 11 12 13 14 15

360360

7.函数返回数组变量

[~/shell/function]# cat array1.sh 

#!/bin/bash

a=(11 12 13 14 15)

function array(){

  echo parameters : "$@" 

  local newarray=(`echo "$@"`)

  local element="$#"

  local i

  for (( i = 0; i < $element; i++ ))

  {

    newarray[$i]=$[ ${newarray[$i]} * 2 ]    

  }

  echo  new value:${newarray[*]}

}

result=`array ${a[*]}`

echo ${result[*]}

[~/shell/function]# ./array1.sh 

parameters : 11 12 13 14 15 new value:22 24 26 28 30