函數可以在shell script當中做一個類似自定義執行命令，最大的功能就是可以簡化我們很多的程序代碼。需要注意的是shell script的執行方式是由上而下/由左而右，因此在shellscript當中的function的設置一定要在程序的最前面，這樣才能夠在執行時被找到可用的程序段。

代碼如下:
#!/bin/bash
# Program
#    This program is to show the use of "function"
# History
# 2013/5/4 by Lvcy First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/loacl/sbin:~/bin
export PATH
 
#輸出統一信息
function printInfo ()
{
        echo -n "Your choice is "
}
#將小寫字符轉換為大寫字符
function dotr()
{
        tr 'a-z' 'A-Z'
}
read -p "Please input your choice(one|two|three|four):" num
#用case做條件判斷
case $num in
        "one")
                printInfo; echo $num | dotr
                ;;
        "two")
                printInfo; echo $num | dotr
                ;;
        "Three")
                printInfo; echo $num | dotr
                ;;
        "four") printInfo; echo $num | dotr
                ;;
esac
exit 0

下面是一個一般的帶有function函數的shell腳本：

代碼如下:
#!/bin/bash
# Program
#    This program is show the params of function
# History
#    2013/5/14 by Lvcy First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
function printInfo()
{
        echo "Your choice is $1"
}
case $1 in
        "one")
                printInfo 1
                ;;
        "two")
                printInfo 2
                ;;