linux下shell脚本编写

if then fi 语句
语句的基本结构：

    if
    then
    elif
    then
    ……
    else
    fi

判断文件的类型（if then fi语句）？

    #!/bin/bash
    Check_file(){
            if
            [ "$1" "$2" ]
            then
            echo "$1" is $3
            exit 0
            fi
    }
    if
    [ "$#" -ne "1" ]
    then
            echo "please input a file follow script"
    elif
    [ ! -e "$1" ]
    then
            echo "$1 is not exist !!"
    else
            Check_file -L $1 link
            Check_file -f $1 "common file"
            Check_file -S $1 socket
            Check_file -b $1 block
            Check_file -c $1 character
            Check_file -d $1 directory
    fi

文件创建用户？
要求:
1.文件数量不对报错
2.文件不存在
3.文件行数有差异
4.用户存在时显示用户存在，但不改变次用户密码
5.当用户不存在时建立用户并设定相应密码

    #!/bin/bash
    if
            [ "$#" != "2" ]
    then
            echo "please input filename and passwdfile after script!!"
            exit 1
    elif
            [ ! -e "$1" ]
    then
            echo "$1 is not exist"
            exit 1
    elif
            [ ! -e "$2" ]
    then
            echo "$2 is not exist"
            exit 1
    elif
            USER_COUNT=`awk 'BEGIN{n=0}{n++}END{print n}' $1`
            PASS_COUNT=`awk 'BEGIN{n=0}{n++}END{print n}' $2`
    then
            echo "用户和密码不匹配"
            exit 1
    fi

    for LINE_NUM in `seq 1 $USER_COUNT`
    do
            USERNAME=`sed -n "${LINE_NUM}p" $1`
            PASSWD=`sed -n "${LINE_NUM}p" $2`
            useradd $USERNAME && {
                    echo $PASSWD | passwd --stdin $USERNAME &>/dev/null && echo $USERNAME is created !!
            }
    done

输入cat输出dog，输入dog输出cat，其他都输出error？

    if
            [ "$1" = "cat" ]
    then
            echo dog
    elif
            [ "$1" = "dog" ]
    then
            echo cat
    else
            echo error
    fi

case语句

自动应答工具expect
ssh自动应答连接？

    #!/usr/bin/expect
    set timeout 5
    set IP   [ lindex $argv 0 ]
    set PASS [ lindex $argv 1 ]
    spawn ssh [e-mail]$IP
    expect {
            "yes/no" { send "yes\r";exp_continue }
            "password" { send "$PASS\r" }
    }
    interact

expect命令调用去执行 .exp文件

ctrl+v ctrl+M 替换文件中的^M=回车键\r
不同作系统命令之间的差异
linux ssdewdw\n
windows safewdw\n\r
unix wqdewd\r

循环中不输出4？

for NUM in {1..10}
do
while [ "$NUM" = 4 ]
do
        continue 4
done
        echo $NUM
done

10秒倒计时？

#!/bin/bash
for (( i=10;i>0;i-- ))
do
        echo -n  "$i's "
        echo -ne "\r"
        sleep 1
done

在执行之后脚本从10s开始倒计时，等倒计时结束之后，脚本执行自动结束

1分10秒倒计时？
方法一：

#!/bin/bash
read -p "please input minute:" m
read -p "please input second:" s
i=$[ m*60+s ]
for (( t=$i;t>0;t-- ))
do
        A=$[ $t/60 ]
        B=$[ $t%60 ]
        echo -ne "\r $A:$B  \r"
        sleep 1
done

方法二：

#!/bin/bash
PRINT_MESSAGE()
{
        echo -n "$MIN:$SEC "
        sleep 1
        echo -ne "\r    \r"
}
MIN=1
SEC=10
for (( ;SEC>=0;SEC-- ))
do
        [ "$SEC" = "0" -a "$MIN" = "0" ]&& exit 0
        [ "$SEC" = "0" -a "$MIN" -gt "0" ]&&{
        PRINT_MESSAGE
        (( MIN-- ))
        SEC=59
        }
        PRINT_MESSAGE
done

脚本实现计算器？
将脚本中的数据导入bc中进行计算，将计算结果输出，数字的运算在bc中运算。

#!/bin/bash
read -p "请输入您要操作的数字：" NUM1
read -p "请输入您要操作的运算：" OP
read -p "请输入要操作的第二个数字：" NUM2
bc <<EOF
$NUM1$OP$NUM2
EOF