Linux shell 学习笔记

echo  ”历经千辛万苦，我终于爬上来了“  

1. Create a multiple line comment:(COMMENT1区间里面的内容为注释)

 

#!/bin/bash

echo "Adding new users to LDAP Server..."

<<COMMENT1

    Master LDAP server : dir1.nixcraft.net.in

    Add user to master and it will get sync to backup server too

    Profile and active directory hooks are below

COMMENT1

echo "Searching for user..."

 

2. Enable debug mode: (可以逐行执行，相当于Win下的echo 打开状态)

bash -x test.sh

 

3. $引用

${SHELL}Code   //隔离开SHELL和Code

echo ${i:=0} //如果i没有被定义则定义为1

echo $(date) //date等命名要（）起来才被认为是命令

 

4. 变量定义：以_或者字母开头

5. 变量与表达式：

1. 算术计算：$((expression))

2. declare -i x=10   //指定x为整型变量

3. 定义常量：readonly var=xxx 或者：declare -r var=xxx

4. 检查变量是否存在：$(var:? Error Message) //var=1,第一参数

5. 比较： > < == !=

6. test -f /aa.txt && cat /aa.txt || echo “file not found”

   //如果存在/aa.txt显示其内容，不存在的话就报预定义的错误。

   // test可以用[]代替，[之后，和]之前要有空格。 test -z $v,检查v是为空

7. Test “$answer” = “yes”  //比较字符串，注意=左右各有空格，要用引号。

8. $? 查看上一个命令执行的返回码，0表示成功。

9. CommandA&&CommandB 逻辑或，A执行成功才执行B;    A||B,A执行失败执行B.

   test $(id -u) -eq 0  && echo "You are root" || echo "NOT root"

10. Logical not: [ ! -d /backup ] && mkdir /backup

11. 大小写转换：echo "TeSt" | tr '[:upper:]' '[:lower:]' 

//或者 var="TesT"   tr '[:upper:]' '[:lower:]' <<<"$var"

12. 检查是否是root  is_user_root(){

 [ "$(id -u)" != "0" ] && die "You must be root to run this script" 2}

     

 

6. 输入输出：

Read:read -t 10 -p "Enter your name : " name // timeout 10s

Redirection:

1. wc -w <<EOF

> This is a test.

> Apple juice.

> 100% fruit juice and no added sugar, colour or preservative.

> EOF

2. wc -w <<<$(netstat -i | cut -d" " -f1 | egrep -v "^Kernel|Iface|lo")

3. sed:  sed ‘/enabled=yes/c\enabled=no’ tftp > tftp.tmp //替换一整行

          sed ‘s/GPGCHECK/gpgcheck/’ tftp >tftp.tmp  //替换关键字

 

7. 正则表达式：

^String 匹配以String开头的行

String$ 匹配以String结尾的行

^.$ 只有一个字符的行;

[numbers] 包含任意一个Number; [a-c] 包含任意一个a到c的字母; [^a-c] 不包含

 

8. 控制语句：

|| if - then语句 ||

if condition

then

Commands

elif condition

then

fi

 

//goto语句，没有，但是可以通过在执行语句中加入$0来实现调用自己。

 

|| case语句 ||

case  $variable-name  in

      pattern1|pattern2|pattern3)       

        command1

          ;;

      pattern4|pattern5|pattern6)

          command1

          ;;            

      [Ss][Qq][Ll])   //匹配SQL大小写形式，可以用shopt -s nocasematch来从

                         //整体上定义。 停止shopt -u nocasematch

        command1

          ;;

      *)              

esac

 

|| Exit select loop ||

select var in a  b c exit //列出1.a    2. b   3.c 让用户选择

do

xxxxxx

Done

 

 

//Until loop

#!/bin/bash

i=1

until [ $i -gt 6 ]

do

echo "Welcome $i times."

i=$(( i+1 ))

done

 

//While loop

While true .OR. :

do

Xxx

Done

 

//For loop

for ((i=0;i<200;i++)) do userdel user$i;done

 

 

 

 

 

 

 

 

 

File attributes comparisons

-a/-e: True if file exists.

-b: True if file exists and is a block special file.

-c: True if file exists and is a character special file.

-d: True if file exists and is a directory.

-f: True if file exists and is a regular file.

-g: True if file exists and is set-group-id.

-h: True if file exists and is a symbolic link.

-k: True if file exists and its ‘‘sticky’’ bit is set.

-p: True if file exists and is a named pipe (FIFO).

-r: True if file exists and is readable.

-s: True if file exists and has a size greater than zero.

-t: True if file descriptor fd is open and refers to a terminal.

-u: True if file exists and its set-user-id bit is set.

-w: True if file exists and is writable.

-x: True if file exists and is executable.

-O: True if file exists and is owned by the effective user id.

-G: True if file exists and is owned by the effective group id.

-L: True if file exists and is a symbolic link.

-S: True if file exists and is a socket.

-N: True if file exists and has been modified since it was last read.

 

File attributes comparisons

#!/bin/bash

echo "The script name : $0"

echo "The value of the first argument to the script : $1"

echo "The value of the second argument to the script : $2"

echo "The value of the third argument to the script : $3"

echo "The number of arguments passed to the script : $#"

echo "The value of all command-line arguments (\$* version) : $*"

echo "The value of all command-line arguments (\$@ version) : $@"

//$* 代表原始的参数， $@ 代表加了IFS之后的参数。

 

 

 

 

 

9. 常用命令：

kill -9 PID

 

 

 

小试：

//9*9 乘法表

 

#!/bin/bash

test $# -eq 0 && n=9 || n=$1

for i in {1..9}

do

if test $n -lt $i

then

continue

fi

for j in {1..9}

do

if test $i -lt $j

then

break

fi

printf "%-4d" $(($i * $j))

Done

printf "\n"

Done

 

//解析文件

 

#!/bin/bash

file=/etc/passwd

## 以：做分隔附读取/etc/passwd各字段分输出 UID>500的记录

while IFS=':' read -r f1 f2 f3 f4 f5 f6 f7

Do

[ $f3 -ge 500 ] && echo -e "\033[31m UserName: \033[32m $f1, \033[31m Enabled: \033[32m `test "$f2" = "x" && echo yes || echo no`, \033[31m USD: \033[32m $f3,\033[31m GID: \033[32m $f4,\033[31m Description: \033[32m $f5,\033[31m HomeDir:\033[32m $f6,\033[31m StartUpShell:\033[32m $f7"

done < "$file"

echo -e "\033[0m"

 

while :; do clear & date +%H:%M:%S & sensors & sleep 2; done //查看温度，先装lm-sensors.

 

 

 

10. 方法：

1. 方法的引用：

source /etc/init.d/function &>/dev/null

echo $? //返回的值是source有没有发现文件

2. 处理CTRL+C

trap '' SIGINT SIGQUIT SIGTSTP