Shell脚本入门

#!/bin/bash
# 基本操作
string="hello world" # 等号前后不能有空格
echo `expr index "$string" lo` # 反引号
for i in "$*"; do # 传入参数
	echo $i
done
for i in "$@"; do
	echo $i
done

# 四则运算
a=3 
b=5 
val=`expr $a + $b` # 运算符前后需要空格,表达式需要加expr
echo "a + b : $val" 
val=`expr $a - $b` 
echo "a - b : $val" 
val=`expr $a \* $b` # 乘法操作需要转义字符
echo "a * b : $val" 
val=`expr $a / $b` 
echo "a / b : $val"

# 关系运算符

if [ $a == $b ] # 相等
then
	echo "a is equal to b"
else
	echo "a is not equal to b"
fi

if [ $a -lt $b ] # 小于
then
	echo "a is less than b"
else
	echo "a is not less than b"
fi

# 字符串运算符
mtext1="hello"
mtext2="world"
mtext3=$mtext1" "$mtext2 # 字符串的拼接
echo $mtext3
echo ${#mtext3} # 输出字符串长度
echo ${mtext3:1:4} # 截取字符串

# 数组操作
array=(a b c d)
val=${array[1]} # 使用$访问变量
echo $val
len=${#array[*]} # 获取数组长度
echo $len

# 输出程序
echo "hello world" > a.txt # 输出重定向到文件
echo `date` # 输出系统时间

# 循环与判断
for i in {1..5} 
do
	if [ `expr $i % 2` -eq 0 ] # 判断偶数
	then
		echo $i
	fi
done

for i in ${array[@]} 
do
	echo $i
	if [ $i = "c" ] # 字符串相等判断
	then
		break # 跳出循环
	fi
done
COUNTER=10
while [ $COUNTER -lt 50 ]
do
	COUNTER=`expr $COUNTER + 10`
	echo $COUNTER
done

# 函数

test1(){
	echo "function test1"
}
test1 

test2(){
	anum=3
	bnum=5
	return $(($anum+$bunm))
}
test2
result=$?
echo $result