Shell (II)

Catalog

  One ：read Read console input

Two ： function

2.1 System function

2.1.1 basename

8.1.2 dirname

2.2 Custom function

3、 ... and ： Getting started with regular expressions

3.1 Regular match

3.2 Special characters are often used

Four ： Text processing tools

4.1 cut

4.2 awk

5、 ... and ： Comprehensive application case

5.1  The archive

5.2  Send a message

---

  One ：read Read console input

1） Basic grammar
read ( Options ) ( Parameters )
① Options ：

-p： Specify the prompt when reading the value ;
-t： Specifies the time to wait while reading the value （ second ） If -t  Not adding means waiting 

② Parameters
Variable ： Specifies the variable name of the read value
2） Case practice

 Tips  7  Seconds , Read the name entered by the console 
[[email protected] shells]$ touch read.sh
[[email protected] shells]$ vim read.sh
#!/bin/bash
read -t 7 -p "Enter your name in 7 seconds :" NN
echo $NN
[[email protected] shells]$ ./read.sh
Enter your name in 7 seconds : atguigu
atguigu

Two ： function

2.1 System function

2.1.1 basename

1） Basic grammar
basename [string / pathname] [suffix] （ Function description ：basename The command will delete all the previous
Including the last （‘/’） character , Then display the string .
basename It can be understood as taking the file name in the path
Options ：
suffix For the suffix , If suffix Designated ,basename Will pathname or string Medium suffix Get rid of .
2） Case practice

 Intercept this /home/atguigu/banzhang.txt  File name of the path .
[[email protected] shells]$ basename /home/atguigu/banzhang.txt
banzhang.txt
[[email protected] shells]$ basename /home/atguigu/banzhang.txt .txt
banzhang

8.1.2 dirname

1） Basic grammar
dirname File absolute path （ Function description ： Remove filename from given filename with absolute path （ Non catalog part ）, Then return to the rest of the path （ Part of the catalog ））dirname It can be understood as the absolute path name of the file path
2） Case practice

 obtain  banzhang.txt  Path to file .
[[email protected] ~]$ dirname /home/atguigu/banzhang.txt
/home/atguigu 

2.2 Custom function

1） Basic grammar

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

2） Experience and skill
（1） Must be before calling function place , Declare function first ,shell The script is run line by line . Not like other languages
Sample compilation first .
（2） Function return value , Only through $? System variable acquisition , Can display plus ：return return , If not , take
Run the result with the last command , As return value .return Heel value n(0-255)
3） Case practice

 Calculate the sum of the two input parameters .
[[email protected] shells]$ touch fun.sh
[[email protected] shells]$ 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 $n2;
[atguigu[email protected] shells]$ chmod 777 fun.sh
[[email protected] shells]$ ./fun.sh
Please input the number1: 2
Please input the number2: 5
7

3、 ... and ： Getting started with regular expressions

Regular expressions are described using a single string 、 Match a series of strings that conform to a certain syntax rule . In many articles
In this editor , Regular expressions are often used for retrieval 、 Replace the text that matches a pattern . stay Linux in ,grep,
sed,awk And other text processing tools support pattern matching through regular expressions .

3.1 Regular match

A string of regular expressions without special characters matches itself , for example ：

[[email protected] shells]$ cat /etc/passwd | grep atguigu

It will match all that contain atguigu The line of .

3.2 Special characters are often used

1） Special characters ：^
^ Match the beginning of a line , for example ：

[[email protected] shells]$ cat /etc/passwd | grep ^a

It will match all of them with a Beginning line

2） Special characters ：$
$ Match the end of a line , for example

[[email protected] shells]$ cat /etc/passwd | grep t$

It will match all of them with t The line at the end

3） Special characters ：.
. Match an arbitrary character , for example

[[email protected] shells]$ cat /etc/passwd | grep r..t

Will match to include rabt,rbbt,rxdt,root And so on
4） Special characters ：*
* Not used alone , He used it with the last character , Means to match the previous character 0 Times or times , for example

[[email protected] shells]$ cat /etc/passwd | grep ro*t

Will match rt, rot, root, rooot, roooot Wait for all the lines

5） Character range （ brackets ）：[ ]
[ ] Means to match a character in a range , for example
[6,8]------ matching 6 perhaps 8
[0-9]------ Match one 0-9 The number of
[0-9]*------ Matches any length of numeric string
[a-z]------ Match one a-z Characters between
[a-z]* ------ Matches an alphabetic string of any length
[a-c, e-f]- matching a-c perhaps e-f Any character between
[[email protected] shells]$ cat /etc/passwd | grep r[a,b,c]*t
Will match rt,rat, rbt, rabt, rbact,rabccbaaacbt Wait, all right
6） Special characters ：\
\ To signify an escape , It will not be used alone . Because all special characters have their own matching patterns , When we want to match
When a particular character itself （ for example , I want to find out all the things that contain '$' The line of ）, There will be difficulties . At this point we will
Use escape characters with special characters , To represent the special character itself , for example

[[email protected] shells]$ cat /etc/passwd | grep ‘a\$b’

It will match all that contain a$b The line of . Note that you need to use single quotes to cause the expression to .

Four ： Text processing tools

4.1 cut

cut The job of “ cut ”, Specifically, it is used to cut data in the file .cut Command from every part of the file
Cut bytes in one line 、 Characters and fields and put these bytes 、 Character and field output .
1） Basic usage

cut [ Option parameters ] filename
 explain ： The default separator is tab 

2） Option parameter description

3） Case practice  

（1） Data preparation 
[[email protected] shells]$ touch cut.txt
[[email protected] shells]$ vim cut.txt
dong shen
guan zhen
wo wo
lai lai
le le
（2） cutting  cut.txt  First column 
[[email protected] shells]$ cut -d " " -f 1 cut.txt
dong
guan
wo
lai
le 
（3） cutting  cut.txt  second 、 The three column 
[[email protected] shells]$ cut -d " " -f 2,3 cut.txt
shen
zhen
wo
lai
le
（4） stay  cut.txt  Cut out in file  guan
[[email protected] shells]$ cat cut.txt |grep guan | cut -d " " -f 1
guan
（5） Selection system  PATH  A variable's value , The first  2  individual “：” All paths after start ：
[[email protected] shells]$ echo $PATH
/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/atguigu/.local/bin:/
home/atguigu/bin
[[email protected] shells]$ echo $PATH | cut -d ":" -f 3-
/usr/local/sbin:/usr/sbin:/home/atguigu/.local/bin:/home/atguigu/bin 
（6） cutting  ifconfig  Post print  IP  Address 
[[email protected] shells]$ ifconfig ens33 | grep netmask | cut -d " " -f 10
192.168.111.101

4.2 awk

A powerful text analysis tool , Read the document line by line , Slice each line with a space as the default separator , Cut open
Then analyze and deal with the part of .
1） Basic usage

awk [ Option parameters ] ‘/pattern1/{action1} /pattern2/{action2}...’ filename
pattern： Express  awk  What to look for in the data , It's a matching pattern 
action： A series of commands executed when a match is found 

2） Option parameter description

3） Case practice  

（1） Data preparation 
[[email protected] shells]$ sudo cp /etc/passwd ./
passwd  What data means 
 user name : password ( Encrypted ): user  id: Group  id: notes : User home directory :shell  Parser 
（2） Search for  passwd  Document to  root  All lines at the beginning of the keyword , And output the  7  Column .
[[email protected] shells]$ awk -F : '/^root/{print $7}' passwd
/bin/bash
（3） Search for  passwd  Document to  root  All lines at the beginning of the keyword , And output the  1  Column and the first  7  Column ,
 In the middle to “,” Division of no. .
[[email protected] shells]$ awk -F : '/^root/{print $1","$7}' passwd
root,/bin/bash
 Be careful ： Only match  pattern  Will be executed  action.
（4） Display only /etc/passwd  The first and seventh columns of , Comma separated , And add column names before all rows  user,
shell  Add on last line "dahaige,/bin/zuishuai".
[[email protected] shells]$ awk -F : 'BEGIN{print "user, shell"}
 {print $1","$7}
END{print "dahaige,/bin/zuishuai"}' passwd
user, shell
root,/bin/bash
bin,/sbin/nologin ...
atguigu,/bin/bash
dahaige,/bin/zuishuai
 Be careful ：BEGIN  Execute before all data read rows ;END  Execute after all data execution .
（5） take  passwd  Users in files  id  Increase in numerical value  1  And the output 
[[email protected] shells]$ awk -v i=1 -F : '{print $3+i}' passwd
1
2
3
4

4）awk Built in variables for

5） Case practice  

（1） Statistics  passwd  file name , Line number of each line , Columns per row 
[[email protected] shells]$ awk -F : '{print "filename:" FILENAME ",linenum:"
NR ",col:"NF}' passwd
filename:passwd,linenum:1,col:7
filename:passwd,linenum:2,col:7
filename:passwd,linenum:3,col:7
... （2） Inquire about  ifconfig  The line number of the empty line in the command output result 
[[email protected] shells]$ ifconfig | awk '/^$/{print NR}'
9
18
26
（3） cutting  IP
[[email protected] shells]$ ifconfig ens33 | awk '/netmask/ {print $2}'
192.168.6.101

5、 ... and ： Comprehensive application case

5.1  The archive

In practical production application , It is often necessary to archive and back up important data .
demand ： Implement a script that archives and backs up the specified directory every day , Enter a directory name （ It doesn't end with /）,
Archive and save all files in the directory on a daily basis , And attach the filing date to the file name , Put it in /root/archive Next .
The archive command is used here ：tar
You can add -c Option means archive , add -z Option means to compress at the same time , The resulting file suffix is .tar.gz.
The script is implemented as follows ：

#!/bin/bash
#  First, judge whether the number of input parameters is  1
if [ $# -ne 1 ]
then
echo " Wrong number of parameters ！ You should enter a parameter , As the archive directory name "
exit
fi
#  Get the directory name from the parameter 
if [ -d $1 ]
then
echo
else
echo
echo " directory does not exist ！"
echo
exit
fi
DIR_NAME=$(basename $1)
DIR_PATH=$(cd $(dirname $1); pwd)
#  Get current date 
DATE=$(date +%y%m%d)
#  Define the name of the generated archive file 
FILE=archive_${DIR_NAME}_$DATE.tar.gz
DEST=/root/archive/$FILE
#  Start archiving catalog files 
echo " Start filing ..."
echo
tar -czf $DEST $DIR_PATH/$DIR_NAME
if [ $? -eq 0 ]
then
echo
echo " Archive success ！"
echo " Archive file is ：$DEST"
echo
else
echo " There is a problem with archiving ！"
echo
fi
exit

5.2  Send a message

We can use Linux Self contained mesg and write Tools , Send messages to other users .
demand ： Implement a script to quickly send messages to a user , Enter the user name as the first parameter , Straight back
Follow the message to be sent . The script needs to detect whether the user logs in to the system 、 Whether to turn on the message function , And the current issue
Whether the sending message is empty .
The script is implemented as follows ：

#!/bin/bash
login_user=$(who | grep -i -m 1 $1 | awk '{print $1}')
if [ -z $login_user ]
then
echo "$1  Not online ！"
echo " Script exit .."
exit
fi
is_allowed=$(who -T | grep -i -m 1 $1 | awk '{print $2}')
if [ $is_allowed != "+" ]
then
echo "$1  No message function is enabled "
echo " Script exit .."
exit
fi
if [ -z $2 ]
then
echo " No message was sent "
echo " Script exit .."
exit
fi
whole_msg=$(echo $* | cut -d " " -f 2- )
user_terminal=$(who | grep -i -m 1 $1 | awk '{print $2}')
echo $whole_msg | write $login_user $user_terminal
if [ $? != 0 ]
then
echo " fail in send ！"
else
echo " Send successfully ！"
fi
exit