Linux in shell scripts

Linux in shell scripts

Stream: flow created by redirecting an input connected to the output
0: Input <
1: standard output>
2: Error Output
ls // aabb 1> test 2> & 1: standard output and standard error file to the test output redirection

>覆盖   >>追加

read aa << AABB end when faced with AABB

Note: read line feed sensitive, can only read the first row

#variable

$ Is to get the value of a variable in Linux

$?
[Root @ root ~] # [9 -ne 9]
[root @ root ~] # echo $?
1

Small script exercises

Enter a number (use the switch) "" "" "

#!/bin/bash
while :
do
echo "输入1-4的数字"
echo '你输入的数字为'
read num
case $num in 
	1) echo '你选择了1'
	;;
	 2) echo '你选择了2'
        ;;
	 3) echo '你选择了3'
        ;;
	 4) echo '你选择了4'
        ;;
	*)echo "输入有误"
	continue
	;;
	esac
	done

- 1-10 print cycle a value of 3 will be replaced hello world 3

for ((i=1;i<=10;i++))
do
        if [ $i -eq 3 ]
        then
        echo "hello world"
        else
        echo "$i"
        fi
done

Achieved within 10 factorial

factorial=1
for i in `seq  10`
do
factorial=`expr $factorial \* $i`
done
echo "10! = $factorial"

方法二：---------------------------------------------

num=1
for((j=1;j<=10;j++))
do
        num=$((num=num*j))
done
        echo "10的阶乘是$num"

Accumulated number of less than 100

#!/bin/bash
sum=0
for((i=1;i<=100;i++))
do
        sum=$((sum=sum+i))
done
echo "$sum"

Multiplication table

#!/bin/bash
for((i=1;i<=9;i++))
do
        for((j=1;j<=i;j++))
do
        echo -n " $i*$j=`expr $i \* $j`"
done
        echo " "
done
            

==========================================================================

Determining if the random number plus

	while [ 1 ]
do
echo "请猜一个100以内数字："
read a
b=$(( $RANDOM % 100 ))
if [$a -eq $b ]
then
        echo "$b"
        echo "猜对了"
elif [ $a -gt $b]
then
        echo "$b"
        echo "猜大了"
else
        echo "$b"
        echo "猜小了"
fi
done

Small note:

================================================== =
printing process tree and write to abc.file file and view the contents of the file abc.file
pstree >> abc.file
modify the file permissions for all users have the highest authority,
chmod 777

Dhcp   自动分配IP：

===================================================================

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