函数是一个脚本代码块，你可以为其命名并在代码中任何位置重用。要在脚本中使用该代码块时，只要使用所起的函数名就行了（这个过程称为调用函数）。本节将会介绍如何在shell脚本中创建和使用函数

function name {

 commands

}

name() {

commands

}

[root@localhost advanced_shell_script]# cat test1.sh

#!/bin/bash

#using a function in a script

function func1 {

    echo "This is an example of a function"

}

count=

while [ $count -le  ] ;do

    func1

    count=$[ $count +  ]

done

echo "This is the end of the loop"

func1

echo "This is script end"

[root@localhost advanced_shell_script]# ./test1.sh

This is an example of a function

This is an example of a function

This is an example of a function

This is the end of the loop

This is an example of a function

This is script end

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# cat test2.sh

#!/bin/bash

#using the return command in a function

function db1 {

 read -p "Enter a value:" value

echo "doubling the value"

return $[ $value *   ]

}

db1

echo "The new value $?"

[root@localhost advanced_shell_script]# ./test2.sh

Enter a value:

doubling the value

The new value 4

[root@localhost advanced_shell_script]# ./test2.sh       #注意$? 返回函数值必须小于256 ，因此需要另外一种方法

Enter a value:200

doubling the value

The new value 144

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# cat test3.sh

#!/bin/bash

#using the return command in a function

function db1 {

 read -p "Enter a value:" value

#echo "doubling the value"

echo $[ $value * 2  ]               #新函数会用echo语句来显示计算的结果。该脚本会获取dbl函数的输出，而不是查看退出状态码

}

value1=$(db1)

echo "The new value $value1"

[root@localhost advanced_shell_script]# ./test3.sh

Enter a value:

The new value

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# cat test4.sh

#!/bin/bash

#passing parameters to a function

function addem {

if [ $# -eq  ] || [ $# -gt   ];then

    echo -

elif [ $# -eq  ];then

    echo $[ $ *  $ ]

else

    echo $[ $ + $ ]

fi

}

echo -n "Adding 20 and 30:"

value=$(addem  )

echo $value

echo -n "30 *:"

value=$( addem )

echo $value

echo -n "10 20 30:"

value=$(addem   )

echo $value

[root@localhost advanced_shell_script]# ./test4.sh

Adding  and :

 *:

  :-

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# cat test5.sh

#/bin/bash

#trying to access script parameters inside a function

function func1 {

    echo $[ $ * $ ]

}

if [ $# -eq  ];then

    value=$(func1 $ $)

    echo "The result is $value"

else

    echo "Usage:badtest1 a b"

fi

[root@localhost advanced_shell_script]# ./test5.sh

Usage:badtest1 a b

[root@localhost advanced_shell_script]# ./test5.sh

The result is

[root@localhost advanced_shell_script]# 

. 全局变量

全局变量是在shell脚本中任何地方都有效的变量。如果你在脚本的主体部分定义了一个全局变量，那么可以在函数内读取它的值。类似地，如果你在函数内定义了一个全局变量，可以在脚本的主体部分读取它的值。

 . 局部变量

无需在函数中使用全局变量，函数内部使用的任何变量都可以被声明成局部变量。要实现这一点，只要在变量声明的前面加上local关键字就可以了。

[root@localhost advanced_shell_script]# cat test6.sh

#!/bin/bash

#demonstrating the local keyword

function func1 {

    local test1=$[ $test2 * 2  ]

    test3=$[ test2 *  ]

}

test3=

test1=

test2=

func1

echo "$test1 $test2 $test3 "

[root@localhost advanced_shell_script]# vim test6.sh

[root@localhost advanced_shell_script]# ./test6.sh     #局部变量的值  test1 在函数执行后没有被修改，test3 的值在函数执行后，被修改为函数执行的结果

1223340 5 10

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# cat test8.sh

#!/bin/bash

# array variable to function test

function test1 {                  #在向函数传递数组变量的时候，需要将数据变量当做一个整体进行传递,通过$@ 方式 
　　　　　　　　　　　　　　　　　　　　#$@ 将给定的多个参数定义为同一字符串的多个单独的单词,类似  "A" "B"  "C"

 local newarray

 newarray=($(echo $@))

 echo "The new array value is: ${newarray[*]}"

}

function test2 {                   #在向函数传递数组变量时，如果使用 $1 参数，会识别为数组变量的第一个参数。无法完整的传递整个参数。默认不会将传递给函数的数组变量看成一个参数

    local newarray

    newarray=$

    echo "The test2 function valueis: ${newarray[*]}"

}

myarray=(    )

echo "The original array is ${myarray[*]}"

test1 ${myarray[*]}

test2 ${myarray[*]}

[root@localhost advanced_shell_script]# ./test8.sh

The original array is

The new array value is:

The test2 function valueis:

[root@localhost advanced_shell_script]# 

root@localhost advanced_shell_script]# cat test11.sh

#!/bin/bash

#using recursion

function factorial {

    if [ $  -eq  ];then

    echo

    else

    local temp=$[ $ -  ]

    local result=`factorial $temp`

    #return $

    echo $[ $result * $ ]

    fi

}

value=

result=$(factorial $value)

echo "$result"

[root@localhost advanced_shell_script]# bash -x test11.sh

+ value=

++ factorial

++ '['  -eq  ']'

++ local temp=

+++ factorial

+++ '['  -eq  ']'

+++ local temp=

++++ factorial

++++ '['  -eq  ']'

++++ local temp=

+++++ factorial

+++++ '['  -eq  ']'

+++++ local temp=

++++++ factorial

++++++ '['  -eq  ']'

++++++ echo

+++++ local result=

+++++ echo

++++ local result=

++++ echo

+++ local result=

+++ echo

++ local result=

++ echo

+ result=

+ echo 

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# cat myfuncs   #创建的库文件需要有执行权限

#my script functions

function addem {

    echo $[ $ + $ ]

}

function multem {

    echo $[ $ * $ ]

}

function divem {

    if [ $ -ne  ];then

        echo $[ $ / $ ]

    else

    echo

    fi

}

[root@localhost advanced_shell_script]# cat test12.sh

#!/bin/bash

# using functions defined in a library file

source ./myfuncs   #两种方式调用库文件 ,source 和 ..  ，这是让库文件在当前shell 调用。如果使用 ./mufuncs 相当于在子shell 调用了。会找不到命令
# ../myfuncs

value1=

value2=

result1=$(addem $value1 $value2)

result2=$(multem $value1 $value2)

result3=$(divem $value1 $value2)

echo "The result of adding them is: $result1"

echo "The result of multiplying them is: $result2"

echo "The result of dividing them is: $result3"

#

[root@localhost advanced_shell_script]# ./test12.sh

The result of adding them is:

The result of multiplying them is:

The result of dividing them is:

[root@localhost advanced_shell_script]# 

[root@localhost advanced_shell_script]# function funcs {  #当在命令行上定义函数时，你必须记得在每个命令后面加个分号，这样shell就能知道在哪里是命令的起止了

> echo $[ $ + $  ];}

[root@localhost advanced_shell_script]# funcs  

[root@localhost advanced_shell_script]# 

[root@localhost ~]# cat /root/.bashrc     # .bashrc 是函数的最佳定义位置

# .bashrc

# User specific aliases and functions

alias rm='rm -i'

alias cp='cp -i'

alias mv='mv -i'

# Source global definitions

if [ -f /etc/bashrc ]; then

    . /etc/bashrc

fi

function add {

    echo $[ $ + $ ]

}

[root@localhost ~]# 

root@localhost advanced_shell_script]# cat test13.sh

#!/bin/bash

source /root/.bashrc    #通过source 命令将函数调用进来，否则命令找不到

result=$(add  )

echo "$result"

[root@localhost advanced_shell_script]#