Linux Shell (2)

function

System function

basename

• basic grammar

  basename [string / pathname] [suffix] Function description: The basename command will delete all prefixes including the last ('/') character, and then display the string

  basename can be understood as the file name in the path file

  Options:

  suffix is ​​the suffix. If suffix is ​​specified, basename will remove suffix from pathname or string.

• Case practice

  Intercept the file name of the /home/guozihan/banzhang.txt path

  [guozihan@hadoop100 program]$ basename /home/guozihan/banzhang.txt
  banzhang.txt
  [guozihan@hadoop100 program]$ basename /home/guozihan/banzhang.txt .txt
  banzhang
  

dirname

• basic grammar

  dirname file absolute pathFunction description: Remove the file name (non-directory part) from the given file name containing an absolute path, and then return the remaining path (directory part)

  dirname can be understood as the absolute path name of the file path

• Case practice

  Get the path of banzhang.txt file

  [guozihan@hadoop100 program]$ dirname /home/guozihan/banzhang.txt
  /home/guozihan
  

Custom function

• basic grammar

  [ function ] funname[()]
  {
        
        
  	Action;
  	[return int;]
  }
  

• experience skills

  • The function must be declared before calling the function, and the shell script is run line by line. It will not be compiled first like other languages.
  • The function return value can only be obtained through the $? system variable. You can add: return to display. If not, the result of the last command will be used as the return value. return followed by the value n(0-255)

• Case practice

  Calculate the sum of two input parameters

  [guozihan@hadoop100 program]$ touch fun.sh
  [guozihan@hadoop100 program]$ vim fun.sh 
  

  #!/bin/bash
  function sum()
  {
        
        
  s=0
  s=$[$1+$2]
  echo "$s"
  }
  read -p "Please input the number1: " n1;
  read -p "Please input the number2: " n2;
  sum $n1 $n2;
  

  [guozihan@hadoop100 program]$ chmod 777 fun.sh
  [guozihan@hadoop100 program]$ ./fun.sh 
  Please input the number1:2
  Please input the number2:5
  7
  

Getting Started with Regular Expressions

Regular expressions use a single string to describe and match a series of strings that conform to a certain grammar rule.. In many text editors, regular expressions are often used to retrieve and replace text that matches a certain pattern.In Linux, text processing tools such as grep, sed, and awk all support pattern matching through regular expressions.。

regular match

A regular expression that does not contain special characters matches itself

[guozihan@hadoop100 program]$ cat /etc/passwd | grep guozihan
guozihan:x:1000:1000:Guozihan:/home/guozihan:/bin/bash

will match all lines containing guozihan

Commonly used special characters

• Special characters: ^

  ^ matches the beginning of a line

  [guozihan@hadoop100 program]$ cat /etc/passwd | grep ^a
  adm:x:3:4:adm:/var/adm:/sbin/nologin
  abrt:x:173:173::/etc/abrt:/sbin/nologin
  avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin
  

  will match all lines starting with a

• Special characters: $

  $ matches the end of a line

  [guozihan@hadoop100 program]$ cat /etc/passwd | grep t$
  halt:x:7:0:halt:/sbin:/sbin/halt
  

  will match all lines ending with t

• Special characters:.

  . matches any character

  [guozihan@hadoop100 program]$ cat /etc/passwd | grep r..t
  root:x:0:0:root:/root:/bin/bash
  operator:x:11:0:operator:/root:/sbin/nologin
  ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
  

  Will match all lines containing rabt, rbbt, rxdt, root, etc.

• Special characters:*

  * is not used alone. It is used together with the previous character to match the previous character 0 or more times.

  [guozihan@hadoop100 program]$ cat /etc/passwd | grep ro*t
  root:x:0:0:root:/root:/bin/bash
  operator:x:11:0:operator:/root:/sbin/nologin
  abrt:x:173:173::/etc/abrt:/sbin/nologin
  rtkit:x:172:172:RealtimeKit:/proc:/sbin/nologin
  

  Will match all lines such as rt, rot, root, rooot, roooot etc.

• Character interval (square brackets): [ ]

  [ ] means match a character within a certain range

  [6,8]------match 6 or 8

  [0-9]------match a number from 0-9

  [0-9]*------matches any length of numeric string

  [az]------matches a character between az

  [az]* ------match any length of alphabetic string

  [ac, ef] - matches any character between ac or ef

  [guozihan@hadoop100 program]$ cat /etc/passwd | grep r[a,b,c]*t
  operator:x:11:0:operator:/root:/sbin/nologin
  abrt:x:173:173::/etc/abrt:/sbin/nologin
  rtkit:x:172:172:RealtimeKit:/proc:/sbin/nologin
  sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
  

  Will match all lines such as rt, rat, rbt, rabt, rbact, rabccbaaacbt, etc.

• Special characters:\

  \ represents escape and will not be used alone. Since all special characters have their own specific matching patterns, we will encounter difficulties when we want to match a special character itself (for example, I want to find all lines containing '$'). at this timeWe need to use escape characters and special characters together to represent the special characters themselves

  [guozihan@hadoop100 program]$ cat /etc/passwd | grep 'a\$b'
  

  will match all lines containing a$b. Note that you need to use single quotes to surround the expression

text processing tools

cut

The job of cut is to "cut", specificallyResponsible for cutting data in the file. cut commandCut bytes, characters and fields from each line of the file and output these bytes, characters and fields。

• Basic usage

  cut [option parameter] filename

  Note: The default delimiter is tab

• Option parameter description

  -f Column number, which column to extract +

  -d Delimiter, split columns according to the specified delimiter, the default is the tab character "\t"

  -c After cutting by characters, add n to indicate which column to take, such as -c 1

• Case practice

  data preparation

  [guozihan@hadoop100 program]$ touch cut.txt
  [guozihan@hadoop100 program]$ vim cut.txt
  

  dong shen
  guan zhen
  wo wo
  lai lai
  le le
  

  Cut the first column of cut.txt

  [guozihan@hadoop100 program]$ cut -d " " -f 1 cut.txt
  dong
  guan
  wo
  lai
  le
  

  Cut the second and third columns of cut.txt

  [guozihan@hadoop100 program]$ cut -d " " -f 2,3 cut.txt
  shen
  zhen
  wo
  lai
  le
  

  Cut out guan in cut.txt file

  [guozihan@hadoop100 program]$ cat cut.txt | grep guan | cut -d " " -f 1
  guan
  

  Select the system PATH variable value, all paths starting with the second ":"

  [guozihan@hadoop100 program]$ echo $PATH
  /usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/guozihan/.local/bin:/home/guozihan/bin
  [guozihan@hadoop100 program]$ echo $PATH | cut -d ":" -f 3-
  /usr/local/sbin:/usr/sbin:/home/guozihan/.local/bin:/home/guozihan/bin
  

  IP address printed after cutting ifconfig

  [guozihan@hadoop100 program]$ ifconfig ens33 | grep netmask | cut -d " " -f 10 
  192.168.182.100
  

awk

A powerful text analysis tool,Read the file line by line, slice each line using spaces as the default delimiter, and then analyze and process the cut parts.。

• Basic usage

  awk [option parameters] '/pattern1/{action1} /pattern2/{action2}…' filename

  Pattern: Indicates what awk is looking for in the data, which is the matching pattern.

  action: a series of commands executed when matching content is found

• Option parameter description

  -F Specify input file delimiter

  -v Assign a value to a user-defined variable

• Notice

  Only rows matching pattern will execute the action.

  [atguigu@hadoop101 shells]$ awk -F : 'BEGIN{print "user, shell"} {print $1","$7} END{print "dahaige,/bin/zuishuai"}' passwd
  user, shell
  root,/bin/bash
  bin,/sbin/nologin 。。。
  atguigu,/bin/bash
  dahaige,/bin/zuishuai
  

  BEGIN is executed before all rows of data are read; END is executed after all data is executed.

• awk's built-in variables

  FILENAME file name

  NR Number of records read (Line number）

  NF The number of domains in the browsing record (After cutting, the number of columns）

• Practical examples

  Query the line number of the blank line in the ifconfig command output result

  [guozihan@hadoop100 program]$ ifconfig | awk '/^$/{print NR}'
  9
  18
  25
  

  Cut IP

  [guozihan@hadoop100 program]$ ifconfig ens33 | awk '/netmask/ {print $2}'
  192.168.182.100
  

Comprehensive application cases

archive file

In actual production applications, important data often need to be archived and backed up.

Requirements: Implement a script that archives backups of a specified directory every day, enter a directory name (without / at the end), archive and save all files in the directory by day, append the archive date to the archive file name, and place it in /root/ archive.

The archive command is used here: tar

You can add the -c option afterwards to indicate archiving, and the -z option to indicate simultaneous compression. The resulting file suffix is ​​.tar.gz.

#!/bin/bash
# 首先判断输入参数个数是否为 1
if [ $# -ne 1 ]
then
echo "参数个数错误！应该输入一个参数，作为归档目录名"
exit
fi
# 从参数中获取目录名称
# 判断目录是否存在
if [ -d $1 ]
then
echo
else
echo
echo "目录不存在！"
echo
exit
fi
DIR_NAME=$(basename $1)
DIR_PATH=$(cd $(dirname $1); pwd)
# 获取当前日期
DATE=$(date +%y%m%d)
# 定义生成的归档文件名称
FILE=archive_${DIR_NAME}_$DATE.tar.gz
DEST=/root/archive/$FILE
# 开始归档目录文件
echo "开始归档..."
echo
tar -czf $DEST $DIR_PATH/$DIR_NAME
if [ $? -eq 0 ]
then
echo
echo "归档成功！"
echo "归档文件为：$DEST"
echo
else
echo "归档出现问题！"
echo
fi
exit

Send a message

We can use the mesg and write tools that come with Linux to send messages to other users

Requirement: Implement a script to quickly send a message to a user. Enter the user name as the first parameter, followed directly by the message to be sent. The script needs to detect whether the user is logged in to the system, whether the messaging function is turned on, and whether the currently sent message is empty.

#!/bin/bash
login_user=$(who | grep -i -m 1 $1 | awk '{print $1}')
# [ -z $变量] :判断变量是否为空
if [ -z $login_user ]
then
echo "$1 不在线！"
echo "脚本退出.."
exit
fi
is_allowed=$(who -T | grep -i -m 1 $1 | awk '{print $2}')
# 查看用户是否开启消息功能
# 判is_allowed是否为+
if [ $is_allowed != "+" ]
then
echo "$1 没有开启消息功能"
echo "脚本退出.."
exit
fi
# 确认有消息发送
if [ -z $2 ]
then
echo "没有消息发出"
echo "脚本退出.."
exit
fi
# 从参数中获取要发送的消息
whole_msg=$(echo $* | cut -d " " -f 2- )
# 获取用户登录的终端
user_terminal=$(who | grep -i -m 1 $1 | awk '{print $2}')
# 写入要发送的数据
echo $whole_msg | write $login_user $user_terminal
# 确认发送结果
if [ $? != 0 ]
then
echo "发送失败！"
else
echo "发送成功！"
fi
exit