1. Define the function inside the shell file and reference it:
[~/shell/function]# cat factorial.sh
#!/bin/bash
function factorial
{
factorial=1
for (( i=1;i <= $1;i++ ))
do
factorial=$[ $factorial * $i ]
done
echo The factorial of $1 is: $factorial
}
echo 'program name': $0, used to find the factorial
factorial $1
[~/shell/function]# ./factorial.sh 10
Program name: ./factorial.sh, the factorial used to find
the factorial 10 is: 3628800
2. Return value
The function return code refers to the status code of the last command of the function, which can be used for the function return value.
Use the return command to manually specify the return value:
[~/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
Since the maximum shell status code is 255, an error occurs when the return value is greater than 255.
[~/shell/function]# ./return.sh
enter a: 200
print 2a: return value 144
3. Function output
To return numbers greater than 255, floats, and string values, it is best to use functions to output to variables:
[~/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