Linux Shell函數方法簡介
linuxcCentOSDebianFreeBSD
1. 在shell文件內部定義函數並引用：
[~/shell/function]# cat factorial.sh
#!/bin/bash
function factorial
{
factorial=1
for (( i=1;i <= $1;i++ ))
do
factorial=$[ $factorial * $i ]
done
echo $1的階乘是:$factorial
}
echo '程序名':$0,用於求階乘
factorial $1
[~/shell/function]# ./factorial.sh 10
程序名:./factorial.sh,用於求階乘
10的階乘是:3628800
2.返回值
函數返回碼是指函數最後一條命令的狀態碼,可以用於函數返回值
使用return命令手動指定返回值：
[~/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
由於shell狀態碼最大是255，所以當返回值大於255時會出錯
[~/shell/function]# ./return.sh
enter a: 200
print 2a: return value 144
3.函數輸出
為了返回大於255的數、浮點數和字符串值，最好用函數輸出到變量：
[~/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.向函數傳遞參數(使用位置參數)：
[~/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.全局變量與局部變量
默認條件下，在函數和shell主體中建立的變量都是全局變量，可以相互引用，當shell主體部分與函數部分擁有名字相同的變量時，可能會相互影響，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
在這種情況下，在函數內部最好使用局部變量，消除影響
[~/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.向函數傳遞數組變量：
[~/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 ${a[*]}
[~/shell/function]# ./array.sh
11 12 13 14 15
parameters : 11 12 13 14 15
360360
7.函數返回數組變量
[~/shell/function]# cat array1.sh
#!/bin/bash
a=(11 12 13 14 15)
function array(){
echo parameters : "$@"
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
