Shell脚本快速入门(2)

sum=`expr 1 + 1`
echo $sum

a=1
b=2
# 加法
val=`expr $a + $b`
echo "$a+$b=$val"

# 减法
val=`expr $a - $b`
echo "$a-$b=$val"

# 乘法
val=`expr $a \* $b` # 必须转义
echo "$a*$b=$val"

# 除法
val=`expr $a / $b`
echo "$a/$b=$val"

# 取余
val=`expr $a % $b`
echo "$a%$b=$val"

a=10
b=20

if [ $a -eq $b ]
then
	echo "$a=$b"
else
	echo "$a!=$b"
fi

a=1
b=2

if [ $a != $b ]
then
	echo "1!=2"
else
	echo "1=2"
fi

if [ $a -gt 0 -o $b -gt 0 ]
then
	echo "a或b大于0"
else
	echo "a和b都不大于0"
fi

if [ $a -gt 0 -a $b -gt 0 ]
then
	echo "a和b都大于0"
else
	echo "a和b不都大于0"
fi

a="hello"
b="world"

if [ $a = $b ]
then
	echo "$a和$b相同"
else
	echo "$a和$b不同"
fi

if [ -z $a ]
then
	echo "$a长度为0"
else
	echo "$a长度不为0"
fi

if [ -n $a ]
then
	echo "$a长度不为0"
else
	echo "$a长度为0"
fi

if [ $a ]
then
	echo "$a不为空"
else
	echo "$a为空"
fi

file="/etc/passwd"

if [ -d $file ]
then
	echo "$file是目录"
else
	echo "$file不是目录"
fi

if [ -f $file ]
then
	echo "$file是普通文件"
else
	echo "$file不是普通文件"
fi

if [ -e $file ]
then
	echo "$file存在"
else
	echo "$file不存在"
fi

if condition
then
	 语句1
	 语句2
	 ...
	 语句N
elif condition2
then
	 语句1
	 语句2
	 ...
	 语句N
else
	 语句1
	 语句2
	 ...
	 语句N
fi

a=1
b=2
if [ $a == $b ]
then
   echo "a = b"
elif [ $a -gt $b ]
then
   echo "a > b"
elif [ $a -lt $b ]
then
   echo "a < b"
else
   echo "所有条件都不匹配"
fi

for item in item1 item2 ... itemN
do
	语句1
	语句2
	...
	语句N
done

for dir in `ls /etc`
do
	echo "$dir"
done

while condition
do
	语句1
	语句2
	...
	语句N
done

c=1
while(( $c<=10 ))
do
    echo $c
		c=`expr $c + 1`
done

case 值 in
模式1)
	语句1
	语句2
	...
	语句N
	;;
模式2)
	语句1
	语句2
	...
	语句N
	;;
*)
	语句1
	语句2
	...
	语句N
	;;
easc

echo '输入星期几'
read day
case $day in
	1)
		echo "星期一"
		;;
	2)
		echo "星期二"
		;;
	...
	*)
		echo "输入的数字无效"
		;;

sum=0

while read n
do
	if [ $n -gt 0 ]
	then
		sum=`expr $sum + $n`
	else
		break
	fi
done

sum=0

while read n
do
	if [ $n -gt 0 ]
	then
		sum=`expr $sum + $n`
	else
		continue # 本次输入不合法，跳过，
	fi
done

#!/bin/bash

i=1

while [ $i -le 9 ] # i <= 9
do
	j=1
	while [ $j -le 9 ] # j <= 9
	do
		if [ $i -ge $j ] # if($i >= $j)
		then
			val=`expr $i \* $j`
			echo -n "$j*$i=$val "
		fi
		j=`expr $j + 1` # j++
	done
	echo
	i=`expr $i + 1` # i++
done