shell脚本编程

shell脚本编程

1.执行的基本流程

(1) vi helloworld
---
#!/bin/bash

echo "hello world!"

(2) chmod +x

(3) ./helloworld

2.顺序执行

---
#!/bin/bash

echo "hello world!"
echo "1"
echo "2"
echo "3"
echo "4"

3.shell 变量

---
#!/bin/bash

read a
read b
c=`expr $a + $b`
echo $c

---
#!/bin/bash

echo $PATH

---
#!/bin/bash
read a
read b
c=$a+$b
echo $c

a=1 b=2 打印出结果1+2

---
#!/bin/bash

declare -i a
declare -i b
declare -i c

read a
read b
c=$a+$b
echo $c

1 1
结果2

---
#!/bin/bash

declare -i c
read a
read b
c=$a+$b
echo $c
数据类型由被赋值对象决定

4.shell特殊字符

#
---
#!/bin/bash
#!/bin/sh

#!/bin/sh
# 井号是一种代码注释
# echo "hello!"

$
---
#!/bin/bash
outputs = "hello world"
echo $outputs --- hello world
echo outputs --- outputs

---
vi ./add

./add 1 2 3 4

./add a "b c" d

#!/bin/bash
echo $*
echo $@

for arg in "$*"
do
echo "---"
echo $arg 只输出一次 1234
done

echo "=-=-=-=-=-"

for arg in "$@"
do
echo "---"
echo $arg 输出四次
done

for arg in $*
do
echo "---"
echo $arg 只输出一次 1234
done

echo "=-=-=-=-=-"

for arg in $@
do
echo "---"
echo $arg 输出四次
done

---
#!/bin/bash

echo $#
echo $0
echo $1
echo $2
echo $3

---
#!/bin/bash

echo 'date'
echo `date`
echo "hello \` "
echo "this is \$str "

5. if

---
#!/bin/bash

if [ $# = 1 ] ; then
_ _ _
echo "input num = 1"
fi

---
#!/bin/bash

if [ $# = 1 ]

then
_ _ _
echo "input num = 1"
fi

if [ $# = 1 ]
then
_ _ _
echo "input num = 1"
else
echo "input num != 1"
fi

---
#!/bin/bash

if [ $# = 1 ]
_ _ _
then
echo "input num = 1"
fi

if [ $# = 1 ]
_ _ _
then
echo "input num = 1"
elif [ $# = 2]
then
echo "input num = 2"
else
echo "input !=1 !=2"
fi

---
vi ./if

#!/bin/bash

if [ $1 = $2 ]
then
echo "$1 = $2"
fi

if [ $1 -eq $2] // ./if a a 会报错 要求参数能转换为数字
then
echo "$1 = $2"
fi

-le <=
-lt <
-ge >=
-gt >

 

---
#!/bin/bash
if [ -f $3 ]
then
echo "文件 \$3 存在"
fi

---
#!/bin/bash

if [ -x $3 ]
then
echo "文件是可执行文件"
fi

---
#!/bin/bash
if [ -d $3 ]
then
echo " \$3 目录存在"
fi

---
#!/bin/sh
if [ ! -d $3 ]
— — — — —
then
echo "\$3 目录不存在"

 

6. shell if 实现计算器脚本

./cal 1 add 2
./cal 1 sub 2
./cal 1 mul 2
./cal 1 div 2

---
#!/bin/bash

if [ $# = 3]
then
else
fi

---
if [ $2 = "add" ]
then
c=`expr $1 + $23`
elif [ $2 = "sub" ]
then
c=`expr $1 - $23 `
elif [ $2 = "mul" ]
then
c=`expr=$1 * $3`
elif [ $2 = "div" ]
then
c=`expr= $1 /$3`
else
echo "不能进行运算"
fi

---
#!/bin/bash

if [ #$ = 3 ]
then
op=$2
op_a=$1
op_b=$3

if [ $op = "add" ]
then
c=`expr $op_a + $op_b`
elif [ $op = "sub" ]
then
c=`expr $op_a - $op_b`
elif [ $op = "mul" ]
then
c=`expr $op_a \* $op_b` #转义字符
echo " \$c"
elif [ $op = "div" ]
c=`expr $op_a / $op_b`
else
echo "没有这个操作符"
fi
echo $c
else
echo "wrong param"
fi

if 的三个空格

 

7. case... 实现分支

---
#!/bin/sh

if [ #$ = 3 ]
then
op = $2
op_a = $1
op_b = $3

case $op in
add)
c=`expr $op_a + $op_b `
echo "$op_a + $op_b = $c"
;;
sub)
c=`expr $op_a - $op_b `
echo "$op_a - $op_b = $c"
;;
mul)
c=`expr $op_a \* $op_b ` # * 需转义
echo "$op_a * $op_b = $c"
;;
div)
c=`expr $op_a / $op_b `
echo "$op_a / $op_b = $c"
;;
*)
echo "no opt"
;;
esac

else
echo "wrong param"
fi

8. shell 循环 loop

集合:
ls 、 find

生成集合:
生成1-100 // seq 1-100

for
---
#!/bin/bash
declare sum -i = 0
for i in "seq 1 100"
do
sum=$sum+$i
done

for obj in `ls`
do
echo "this is $obj"
done

echo "1+2+3+... ...+100 = $sum"

---

for ((i=1; i<=100; i++))
do
sum=$sum+$i
done

while
---
#!/bin/bash
i=0
while [ $i -le 100 ]
do
sum=$sum+$i
i=`expr $i + 1 `
done

---
#!/bin/bash

i=0
sum=0
while [ i -le 100 ]
do
if [ $i -eq 3 ]
then
i=`expr $i + 1`
continue
fi

if [ $i = 5 ]
then
break
fi

sum=$sum+$i
i=`expr $i + 1`
done

---

9. 函数基础

实现 ./func 1 2 4 3 对输入的参数进行比较 按照从小到大输出

---
#!/bin/bash

if [ $# = 4 ]
then

if [ $1 -le $2 ]
then
echo "$1 $2"
else
echo "$2 $1"
fi

if [ $3 -le $4 ]
then
echo "$3 $4"
else
echo "$4 $3"
fi

else

fi

封装函数
---
#!/bin/bash

function min_max()
{
if [ $# = 2 ]
then
if [ $1 -le $2 ]
then
echo "$1 $2"
else
echo "$2 $1"
fi
return 1
else
return 0
fi
}

if [ $# = 4 ]
then
min_max $1 $2
echo "$?"
min_max $3 $4
echo "$?"
else
echo "useage ./func 1 2 4 3 "
fi

$? 表示函数的返回值,会表示最后一条命令的返回值

 

10. 函数的作用域

---
#!/bin/bash
function min_max()
{
local max #局部变量
echo $max #可以输出 max 是一个整体的变量
if [ $# = 2 ]
then
if [ $1 -le $2 ]
then
echo "$1 $2"
else
echo "$2 $1"
fi
return 1
else
return 0
fi
}

if [ $# = 4 ]
then
max=12345
min_max $1 $2
echo "$?"
min_max $3 $4
echo "$?"
else
echo "useage ./func 1 2 4 3 "
fi

全局变量
---
#!/bin/bash

function min_max()
{
local max #局部变量
echo $max #可以输出 max 是一个整体的变量
if [ $# = 2 ]
then
if [ $1 -le $2 ]
then
#echo "$1 $2"
max=$2
min=$1
else
#echo "$2 $1"
max=$2
min=$1
fi
return 1
else
return 0
fi
}

if [ $# = 4 ]
then
max=$1
min=$2

min_max $1 $2
echo "$?"
echo "$min $max"
min_max $3 $4
echo "$?"
echo "$min $max"
else
echo "useage ./func 1 2 4 3 "
fi

 

---

#!/bin/bash
function min_max()
{ #可以输出 max 是一个整体的变量
if [ $# = 2 ]
then
if [ $1 -le $2 ]
then
echo "$1 $2"
else
echo "$2 $1"
fi
return 1
else
return 0
fi
}

if [ $# = 4 ]
then
val=$(min_max $1 $2)
declare -a array=($val)
echo "array: ${array[0]} ${array[1]}"
echo "return value $?"
echo "array count : ${#array[@]}"

for val in ${array[*]}
do
echo "val $val "
done

min_max $1 $2
echo "$?"
min_max $3 $4
echo "$?"

11. 结束语