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Shell script Basics

2022-06-13 07:39:00 【_ seven seven】

From inside to outside ： Hardware - linux kernel - shell(cd、ls…) - Outer application ;

Shell Parser

1、linux Provided shell Parser ：

$ cat /etc/shells 

/bin/sh
/bin/bash
/sbin/nologin
/bin/dash
/bin/tcsh
/bin/csh

2、bash and sh The relationship between

$ cd /bin/
$ ll | grep bash

-rwxr-xr-x. 1 root root 941880 5 month   11 2016 bash
lrwxrwxrwx. 1 root root      4 5 month   27 2017 sh -> bash

3、Centos Default parser ：bash

$ echo $SHELL

/bin/bash

Shell Script

1、 Script format

Script to #!/bin/bash start , Specify the parser

2、 demand ： establish shell Script , Output helloworld


$ touch helloworld.sh
$ vi helloworld.sh

 stay helloworld.sh Enter the following in 
#! /bin/bash
echo "helloworld test"

Script execution ：

 The first one is ：
 use bash or sh+ Relative or absolute path of script （ Don't assign script +x jurisdiction ）
$ sh helloworld.sh 
$ bash helloworld.sh

 The second kind ：
 Execute the script using the absolute or relative path of the input script （ Must have executable permissions +x）
./helloworld.sh
 If you don't have enough authority  
$ chmod 777 helloworld.sh

Be careful ：

First execution method , The essence is bash Parsers help you execute scripts , So the script itself does not need execution permission .

The second method of execution , The essence is that scripts need to be executed by themselves , Therefore, execution permission is required .

3、 Multiline command processing

（1） demand ：

stay /home/test/ Create one in the directory test.txt, stay test.txt Add to file “I love shell”.

$ touch batch.sh
$ vi batch.sh

 stay batch.sh Enter the following in 
#!/bin/bash

cd /home/test
touch test.txt
echo "I love shell" >>cls.txt

Shell Variable

1、 Common system variables

$H O M E 、$ PWD、 $S H E L L 、$ USER etc.

Check the variable ：

$ echo $HOME
$ echo $PWD
...

2、 Custom variable

1． Basic grammar 
（1） Defining variables ：  Variable = value  
（2） Revoke variables ： unset  Variable 
（3） Declare static variables ： readonly  Variable , Be careful ： You can't  unset

2． Variable definition rules 
（1） Variable names can be alphabetized 、 Numbers and underscores , But it can't start with a number , Environment variable name is recommended to be capitalized .
（2） No spaces on both sides of equal sign !
（3） stay  bash  in , Variable default type is string type , No direct numerical operation .
（4） Value of variable if there is a space , Double or single quotes are required .

（1） Defining variables A

$ A=5
$ echo $A
5

（2） To the variable A Reassign

$ A=8
$ echo $A
8

（3） Revoke variables A

$ unset A
$ echo $A

（4） Declare static variables B=2, You can't unset

$ readonly B=2
$ echo $B
2
B=9
-bash: B: readonly variable

（5） stay bash in , Variable default type is string type , No direct numerical operation

$ C=1+2
$ echo $C
1+2

（6） Value of variable if there is a space , Double or single quotes are required

$ D=I love shell
-bash: world: command not found

$ D="I love shell"
$ echo $D
I love shell

（7） Variable can be promoted to global environment variable , For other purposes Shell Program usage

export Variable name

$ echo $D
I love shell
---

./helloworld.sh
helloworld shell

---
$ vim helloworld.sh 

 stay helloworld.sh Add to file echo $D

#!/bin/bash

echo "helloworld"
echo $D

---

$ ./helloworld.sh 
Helloworld
 Found no printout variables D Value .

---

export D
$ ./helloworld.sh 
helloworld
I love shell

Special variables ：$n

1． Basic grammar

$n （ Function description ：n Is the number ,$0 Represents the script name ,$1- $9 generation surface The first One To The first Nine individual ginseng Count, Ten With On Of ginseng Count, Ten With On Of ginseng Count Need to be want use Big enclosed Number package contain, Such as$ {10}）

2． Case practice
（1） Output the script file name 、 Input parameters 1 And input parameters 2 Value


[[email protected] datas]$ touch parameter.sh 
[[email protected] datas]$ vim parameter.sh

#!/bin/bash
echo "$0 $1 $2"

---

$ chmod 777 parameter.sh
$ ./parameter.sh AA BB
./parameter.sh AA BB

Special variables ：$#

1． Basic grammar
$# （ Function description ： Get the number of all input parameters , Commonly used in cycles ）.

$ vim parameter.sh

#!/bin/bash
echo "$0 $1 $2"
echo $#

---
$ chmod 777 parameter.sh

[[email protected] datas]$ ./parameter.sh AA BB
parameter.sh AA BB
2

Special variables ： $* 、$ @

1． Basic grammar

$* （ work can Sketch Statement ： this individual change The amount generation surface life Make That's ok in the Yes Of ginseng Count,$ * Treat all parameters as a whole ）

$@ （ work can Sketch Statement ： this individual change The amount also generation surface life Make That's ok in the Yes Of ginseng Count, No too$ @ Treat each parameter differently ）

2． Case practice
（1） Print all parameters entered

$ vim parameter.sh

#!/bin/bash
echo "$0 $1 $2"
echo $#
echo $*
echo [email protected]

---
$ bash parameter.sh 1 2 3
parameter.sh 1 2
3
1 2 3
1 2 3

Special variables ：$？

1． Basic grammar
$？（ Function description ： Return status of last executed command . If the value of this variable is 0, Prove that the last command was executed correctly ; If the value of this variable is not 0（ Which number is it , It's up to the order itself ）, The last command was executed incorrectly .）

2． Case practice

（1） Judge helloworld.sh Whether the script is executed correctly

$ ./helloworld.sh 
hello world

$ echo $?
0

Operator

1． Basic grammar

（1）“ $(( Arithmetic expression )) ” or “ $[ Arithmetic expression ] ”

（2）expr + , - , *, /, % Add , reduce , ride , except , Remainder

Be careful ：expr Space between operators

Case practice ：

（1） Calculation 3+2 Value

$ expr 2 + 3
5

（2） Calculation 3-2 Value

$ expr 3 - 2 
1

（3） Calculation （2+3）* 4 Value

（a）expr One step calculation

$ expr `expr 2 + 3` \* 4
20

（b） use $[ Arithmetic expression ] The way

S=$[(2+3)*4]
echo $S

conditional

1、 Basic grammar

[ condition ]（ Be careful condition Space before and after ）

Be careful ： If the condition is not empty, it is true,[ abc ] return true,[] return false.

2、 Common judgment conditions

（1） Compare two integers

=  String comparison 

-lt  Less than （less than）			
-le  Less than or equal to （less equal）

-eq  be equal to （equal）				
-gt  Greater than （greater than）

-ge  Greater than or equal to （greater equal）	
-ne  It's not equal to （Not equal）

（2） Judge according to the file authority

-r  Have read permission （read）			
-w  Have the right to write （write）
-x  Have the authority to execute （execute）

（3） Judge according to the document type

-f  The file exists and is a regular file （file）
-e  File exists （existence）		
-d  The file exists and is a directory （directory）

3、 Case practice

（1）23 Greater than or equal to 22

$ [ 23 -ge 22 ]
$ echo $?
0

（2）helloworld.sh Whether you have write permission

$ [ -w helloworld.sh ]
$ echo $?
0

（3）/home/test/test.txt Does the file in the directory exist

$ [ -e /home/test/test.txt ]
$ echo $?
1

（4） Multi condition judgment （&& Indicates that the previous command is executed successfully , To execute the last command ,|| Indicates that after the execution of the previous command fails , To execute the next command ）

&& echo OK || echo notok
OK

$ [ condition ] && [ ] || echo notok
notok

Process control （ a key ）

if Judge

1． Basic grammar

if [  Conditional judgment  ];then 
	 Program 
fi

 perhaps 

if [  Conditional judgment  ] 
then 
	 Program 
fi

matters needing attention ：

（1）[ Conditional judgment ], There must be a space between the bracket and the conditional judgment

（2）if Space after

Case practice

（1） Enter a number , If it is 1, The output print 1, If it is 2, The output print 2 , If other , Output nothing .

$ touch if.sh
$ vim if.sh


#!/bin/bash

if [ $1 -eq "1" ]
then
	echo "print 1"
elif [ $1 -eq "2" ]
then
	echo "print 2"
fi

$ chmod 777 if.sh 
$ ./if.sh 1

case sentence

1． Basic grammar

case $ Variable name  in 
" value 1"） 
 If the value of the variable is equal to the value 1, Then execute the procedure 1 
;; 
" value 2"） 
 If the value of the variable is equal to the value 2, Then execute the procedure 2 
;; 
… Omit other branches … 
*） 
 If none of the values of the variables are above , Then execute this procedure  
;;
esac

$ chmod 777 case.sh
$ ./case.sh 1
1

for loop

1、 Basic grammar 1

for ((  Initial value ; Cycle control conditions ; Variable change  )) 
do 
	 Program  
done

Case practice

（1） from 1 Add to 100

$ touch for1.sh
$ vim for1.sh


#!/bin/bash

s=0
for((i=0;i<=100;i++))
do
	s=$[$s+$i]
done
echo $s

$ chmod 777 for1.sh 
$ ./for1.sh 
“5050”

2、 Basic grammar 2

for  Variable  in  value 1  value 2  value 3… 
do 
	 Program  
done

（1） Print all input parameters

$ touch for2.sh
$ vim for2.sh

#!/bin/bash
# Print digit 

for i in $*
do
	echo "print $i "
done

$ chmod 777 for2.sh 
$ bash for2.sh aa bb cc

3、 Compare $* and$ @ difference

（a） $* and$ @ Represents all parameters passed to a function or script , Not double quoted “” Inclusion time , Are subject to $1 $2 \dots$ n Output all parameters in the form of .

$ touch for.sh
$ vim for.sh


#!/bin/bash

for i in $*
do
    echo "$* print $i "
done

for j in [email protected]
do
    echo "[email protected] print $j"
done

$ bash for.sh AA BB CC

（b） When they are double quoted “” Inclusion time ,“$*” All parameters will be taken as a whole , With “$1 $2 \dots$ n” Output all parameters in the form of ;“[email protected]” Separate parameters , With “$1” “ $2 ” \dots ”$ n” Output all parameters in the form of .

$ vim for.sh

#!/bin/bash

for i in "$*"
#$* All parameters in are considered as a whole , So this for Loop only once 
do
    echo "ban zhang love $i"
done

for j in "[email protected]"
#[email protected] Each parameter in is considered independent , therefore “[email protected]” There are several parameters in , It's going to cycle a couple of times 
do
    echo "ban zhang love $j"
done

$ chmod 777 for.sh
$ bash for.sh aa bb cc

while loop

1． Basic grammar

while [  Conditional judgment  ]

do
    
     Program 
    
done

Case practice

（1） from 1 Add to 100

[email protected]:~$ touch while.sh
[email protected]:~$ vim while.sh 


#!/bin/bash
s=0
i=1
while [ $i -le 100 ]
do
    s=$[$s+$i]
    i=$[$i+1]
done

echo $s


-rw-rw-r--  1 lyh  lyh    88 Feb 15 18:33 while.sh
[email protected]:~$ bash while.sh
5050

read Read console input

1． Basic grammar

read ( Options ：-p -t) ( Parameters ： Variable )

Options ：

-p： Specify the prompt when reading the value ;

-t： Specifies the time to wait while reading the value （ second ）.

Parameters

Variable ： Specifies the variable name of the read value

Case practice

（1） Tips 7 Seconds , Read the name entered by the console

[email protected]:~/test$ touch read.sh
[email protected]:~/test$ vi read.sh

#!/bin/bash

read -t 7 -p "Enter your name in 7 seconds " NAME
echo $NAME

[email protected]:~/test$ bash read.sh 
Enter your name in 7 seconds lyh
lyh

[email protected]:~/test$ bash read.sh 
Enter your name in 7 seconds 
[email protected]:~/test$

function

1、 System function

1. basename Basic grammar

basename [string / pathname] [suffix]

Function description ：

basename The command deletes all prefixes in the path, including the last one （‘/’） character , Then display the string .

Options ：

suffix For the suffix , If suffix Designated ,basename Will pathname or string Medium suffix Get rid of .

（1） Intercept this /home/lyh/test/test.txt File name of the path

[email protected]:~/test$ touch test.txt

[email protected]:~/test$ basename /home/lyh/test/test.txt 
test.txt

[email protected]:~/test$ basename /home/lyh/test/test.txt .txt
test

2. dirname Basic grammar

dirname  File absolute path

Function description ： Get file path

Remove filename from given filename with absolute path （ Non catalog part ）, Then return to the rest of the path （ Part of the catalog ）

[email protected]:~/test$ dirname /home/lyh/test/test.txt 
/home/lyh/test

[email protected]:~/test$ dirname test.txt 
.

2、 Custom function

Basic grammar

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

（1） Must be before calling function place , Declare function first ,shell The script is run line by line . It doesn't compile first like any other language .

（2） Function return value , Only through $? System variable acquisition , Can display plus ：return return , If not , Results will be run with the last command , As return value .return Heel value n(0-255)

Addition of two numbers ：

[email protected]:~/test$ touch fun.sh
[email protected]:~/test$ vi fun.sh 

#!/bin/bash

function sum()
{
    
    s=0
    s=$[ $1 + $2 ]
    return $s
}

read -p "Please input the number1: " n1;
read -p "Please input the number2: " n2;
sum $n1 $n2;
echo $s;

[email protected]:~/test$ bash fun.sh $n1 $n2
Please input the number1: 5
Please input the number2: 6
11

Shell Tools （ a key ）

1、cut

cut The job of “ cut ”, Specifically, it is used to cut data in the file .cut Command to cut bytes from each line of a file 、 Characters and fields and put these bytes 、 Character and field output .

cut [ Option parameters ]  filename

 Option parameters 
-f  Column number , Extract which column 
-d  Separator , Splits columns according to the specified separator 
 explain ： The default separator is tab

cut: You must specify a set of bytes 、 A list of characters or fields

（0） Data preparation

[email protected]:~/test$ vi test.txt
[email protected]:~/test$ cat test.txt 
AA BB CC
DD,EE,FF
GG|HH|II

（1） cutting test.txt First column

[email protected]:~/test$ cut -f 1 -d " " test.txt
AA
DD,EE,FF
GG|HH|II

（2） cutting test.txt second 、 The three column

[email protected]:~/test$ cut -f 2,3 -d "," test.txt
AA BB CC
EE,FF
GG|HH|II

（3） stay test.txt Cut out in file HH

cut:  You must specify a set of bytes 、 A list of characters or fields 

[email protected]:~/test$ cat test.txt | grep "HH" | cut -f 2 -d "|"
HH

（4） Selection system PATH A variable's value , The first 2 individual “：” All paths after start ：

[email protected]:~/test$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin

[email protected]:~/test$ echo $PATH | cut -d : -f 3
/usr/sbin

[email protected]:~/test$ echo $PATH | cut -d : -f 3-
/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
[email protected]:~/test$

2、sed

sed Is a flow editor , It processes one line at a time . When dealing with , Store the currently processed rows in a temporary buffer , be called “ Mode space ”, Then use sed Command processing buffer contents , After processing , Send the contents of the buffer to the screen . Next line , This is repeated , Until the end of the file . The contents of the document have not changed , Unless you use redirected storage output .

Basic usage

sed [ Option parameters ]  ' command '  filename

 Option parameters 
-e	 Directly in command line mode sed Action editor .

 command 
a 	 newly added ,a You can use a string after , On the next line 
d	 Delete 
s	 Find and replace

（0） Data preparation


[email protected]:~$ touch sed.txt

[email protected]:~$ vim sed.txt 
[email protected]:~$ cat sed.txt 
li lei
lei lei
xiao hong
xiao hei

（1） take “gorgeous” This word is inserted into sed.txt Second elements , Print .


[email protected]:~$ sed '2a gorgeous' sed.txt
li lei
lei lei
gorgeous
xiao hong
xiao hei

[email protected]:~$ cat sed.txt 
li lei
lei lei
xiao hong
xiao hei

 Be careful ： The file hasn't changed

（2） Delete sed.txt All files contain xiao The line of


[email protected]:~$ sed '/xiao/d' sed.txt
li lei
lei lei

[email protected]:~$ cat sed.txt 
li lei
lei lei
xiao hong
xiao hei

（3） take sed.txt In file l Replace with A


[email protected]:~$ sed 's/l/A/g' sed.txt
Ai Aei
Aei Aei
xiao hong
xiao hei

[email protected]:~$ sed 's/l/A/' sed.txt
Ai lei
Aei lei
xiao hong
xiao hei

 Be careful ：‘g’ Express global, All replacement

（4） take sed.txt The second line in the file is deleted and the l Replace with A


[email protected]:~$ sed -e '2d' -e 's/l/A/g' sed.txt 
Ai Aei
xiao hong
xiao hei

[email protected]:~$ sed '2d' 's/l/A/g' sed.txt 
sed:  Can't read  s/l/A/g:  There is no file or directory 
li lei
xiao hong
xiao hei

3、awk

A powerful text analysis tool , Read the document line by line , Slice each line with a space as the default separator , The cut part is analyzed again .


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 

 Option parameters 
-F   Specify the input file separator 
-v   Assign a user-defined variable

（0） Data preparation


[email protected]:~/test$ cp /etc/passwd ./

[email protected]:~/test$ ll
 Total usage  24
drwxrwxr-x  2 lyh lyh 4096 Feb 16 00:00 ./
drwxr-xr-x 16 lyh lyh 4096 Feb 15 23:22 ../
-rw-r--r--  1 lyh lyh 2801 Feb 16 00:00 passwd

[email protected]:/etc$ cat passwd
root:x:0:0:root:/root:/bin/bash
...

（1） Search for passwd Document to root All lines at the beginning of the keyword , And output the 7 Column .

[email protected]:~/test$ awk -F : '/^root/{print $7}' passwd 
/bin/bash

（2） 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]:~/test$ awk -F : '/^root/{print $1","$7}' passwd 
root,/bin/bash

Be careful ： Only match pattern Will be executed action

（3） Display only /etc/passwd The first and seventh columns of , Comma separated , And add column names before all rows beginshell Add on last line endshell.


[email protected]:~/test$ awk -F : 'BEGIN{print "beginshell"}{print $1","$7}END{print "endshell"}' passwd

beginshell
root,/bin/bash
daemon,/usr/sbin/nologin
...
lyh,/bin/bash
systemd-coredump,/usr/sbin/nologin
endshell

Be careful ：BEGIN Execute before all data read rows ;END Execute after all data execution .

（4） take passwd Users in files id（ The third column ） Increase in numerical value 1 And the output

[email protected]:~/test$ cat passwd 
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
...

[email protected]:~/test$ awk -v i=1 -F : '{print $3+i}' passwd
1
2
3
4
...

awk Built in variables for

FILENAME	 file name 
NR	 Number of records read 
NF	 The number of fields in the browsing record （ After cutting , Number of columns ）

（1） Statistics passwd file name , Line number of each line , Columns per row

[email protected]:~/test$ awk -F : '{print FILENAME,NR,NF}' passwd 
passwd 1 7
passwd 2 7
passwd 3 7
passwd 4 7
passwd 5 7
passwd 6 7
passwd 7 7
passwd 8 7
passwd 9 7
passwd 10 7
passwd 11 7
passwd 12 7
passwd 13 7
passwd 14 7
...

（2） Inquire about test.txt Line number of the blank line


[email protected]:~/test$ cat test.txt 
AA BB CC
DD,EE,FF
GG|HH|II

abcd

[email protected]:~/test$ awk '/^$/{print NR}' test.txt 
4

4、sort

Sort the files , And output the sorting result standard .

sort( Options )( Parameters )

 Options ：
-n	 Sort by the size of the value 
-r	 In reverse order 
-t	 Set the separator used for sorting 
-k	 Specify the columns to sort 

 Parameters ： Specify the list of files to sort

（1） according to “：” The third column after splitting is sorted in reverse order .


[email protected]:~/test$ touch sort.sh
[email protected]:~/test$ vim sort.sh
[email protected]:~/test$ cat sort.sh 
AA:40:5.4
BB:20:4.2
CC:50:2.3
DD:10:3.5
EE:30:1.6

[email protected]:~/test$ sort -t : -nr -k3 sort.sh 
AA:40:5.4
BB:20:4.2
DD:10:3.5
CC:50:2.3
EE:30:1.6

common problem ：

problem 1： Use Linux Command query file1 Line number of the blank line


[email protected]:~/test$ awk '/^$/{print NR}' test.txt 
4

problem 2： Documents chengji.txt The contents are as follows :

Zhang San 40

Li Si 50

Wang Wu 60

Use Linux Command to calculate the sum of the second column and output


$ cat chengji.txt | awk -F " " '{sum+=$2} END{print sum}'
150

problem 3：Shell How to check whether a file exists in the script ？ What to do if it doesn't exist ？

#!/bin/bash

if [ -f file.txt ]; then
    echo " File exists !"
else
    echo " file does not exist !"
fi

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当前位置：网站首页>Shell script Basics

Shell script Basics

List of articles

Shell Parser

Shell Script

Shell Variable

Special variables ：$n

Special variables ：$#

Special variables ： $* 、$ @

Operator

conditional

Process control （ a key ）

if Judge

case sentence

for loop

1、 Basic grammar 1

2、 Basic grammar 2

3、 Compare $* and$ @ difference

while loop

read Read console input

function

1、 System function

1. basename Basic grammar

2. dirname Basic grammar

2、 Custom function

Shell Tools （ a key ）

1、cut

2、sed

3、awk

4、sort

common problem ：

problem 1： Use Linux Command query file1 Line number of the blank line

problem 2： Documents chengji.txt The contents are as follows :

problem 3：Shell How to check whether a file exists in the script ？ What to do if it doesn't exist ？

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当前位置：网站首页>Shell script Basics

Shell script Basics

List of articles

Shell Parser

Shell Script

Shell Variable

Special variables ：$n

Special variables ：$#

Special variables ： ∗ 、 *、 ∗、@

Operator

conditional

Process control （ a key ）

if Judge

case sentence

for loop

1、 Basic grammar 1

2、 Basic grammar 2

3、 Compare ∗ and * and ∗ and @ difference

while loop

read Read console input

function

1、 System function

1. basename Basic grammar

2. dirname Basic grammar

2、 Custom function

Shell Tools （ a key ）

1、cut

2、sed

3、awk

4、sort

common problem ：

problem 1： Use Linux Command query file1 Line number of the blank line

problem 2： Documents chengji.txt The contents are as follows :

problem 3：Shell How to check whether a file exists in the script ？ What to do if it doesn't exist ？

边栏推荐

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Special variables ： $* 、$ @

3、 Compare $* and$ @ difference