One . function

shell Will be allowed in A set of commands or sentence Form a section Available code , These blocks of code are called shell function . Give this code a name called function name , You can call the function of this code directly later .

1. Function definition

 Function name ()
{
    
   The body of the function （ A collection of orders , To achieve a function ）   
}

#  You can take function  Function name ()  Definition , It can also be direct   Function name ()  Definition , Without any parameters 

function  Function name ()
{
    
    The body of the function （ A collection of orders , To achieve a function ）  
}

· return explain ：
1.return You can end up with a function , Similar to the loop control statement mentioned earlier break.
2.return The default returns the exit status of the last command in the function , You can also give parameter values , The value range of this parameter is 0-256 Between .
3. without return command , The function will return the last Shell The exit value of .

2. Function call

2.1 Called directly in script

#!/bin/bash
demoFun()
{
    
    echo " This is a shell function !"
}
echo "----- The function starts executing -----"
demoFun
echo "----- The function is finished -----"

2.2 Defined in the user's environment variables

#  When the user opens bash The file will be read when ：
/etc/profile --> /etc/bashrc --> ~/.bash_profile --> ~/.bashrc

#  We can directly define functions in these files to call 

2.3 Current command line call

[root@server ~]# cat test.sh 
#!/bin/bash
demoFun()
{
    
    echo " This is a shell function !"
}

[root@server ~]# source test.sh 
[root@server ~]# demoFun
 This is a shell function !

3. Function arguments

#!/bin/bash
funWithParam()
{
    
    echo " The first parameter is zero  $1 !"
    echo " The second parameter is  $2 !"
    echo " The tenth parameter is  $10 !"
    echo " The tenth parameter is  ${10} !"
    echo " The eleventh parameter is  ${11} !"
    echo " The total number of parameters is  $#  individual !"
    echo " Output all parameters as a string  $* !"
}
funWithParam 1 2 3 4 5 6 7 8 9 34 73

#  stay Shell in , You can pass parameters to a function when you call it .
#  Inside the body of the function , adopt  $n  To get the value of the parameter 

Case study ： Let users enter information , If you don't enter, keep prompting until you enter

#!/bin/bash
input_fun()
{
    
	input_var=""
	output_var=$1
	while [ -z $input_var ]
	do
		read -p "$output_var" input_var
	done
	echo $input_var
}

# Call the function and get the user's name 、 Gender 、 Age is assigned to name、sex、age Variable 
name=$(input_fun  Please enter your name :)
sex=$(input_fun  Please enter your gender :)
age=$(input_fun  Please enter your age :)

#!/bin/bash
input_fun()
{
    
	read -p "$1" name
	if [ -z $name ];then
		fun $1
	else
	echo $name
	fi
}

# Call the function and get the user's name 、 Gender 、 Age is assigned to name、sex、age Variable 
name=$(input_fun  Please enter your name :)
sex=$(input_fun  Please enter your gender :)
age=$(input_fun  Please enter your age :)

Two . random number

1. Grammatical structure

# bash There is one by default $RANDOM The variable of , The default is 0~32767.
set | grep RANDOM	

#  Check the last generated random number 
echo $RANDOM

#  produce 0~1 Random number between 
echo $[$RANDOM%2]

#  produce 0~9 The random number in 
echo $[$RANDOM%10]

#  produce 0~100 The random number in 
echo $[$RANDOM%101]

#  produce 50-100 A random number within 
echo $[$RANDOM%51+50]

#  To produce a three digit random number 
echo $[$RANDOM%900+100]

2. Case study

1) Randomly generated 1000 In a 182 Cell phone number at the beginning

#!/bin/bash
for ((i=1;i<=1000;i++))
do
	n1=$[$RANDOM%10]
	n2=$[$RANDOM%10]
	n3=$[$RANDOM%10]
	n4=$[$RANDOM%10]
	n5=$[$RANDOM%10]
	n6=$[$RANDOM%10]
	n7=$[$RANDOM%10]
	n8=$[$RANDOM%10]
	echo "182$n1$n2$n3$n4$n5$n6$n7$n8" |tee -a phonenum.txt
done

2) Draw lucky viewers

#  Above 1000 Lottery in a cell phone number 5 A lucky audience .
#  It shows that 5 A lucky audience .
#  Show only headers 3 Number and tail number 4 Number , Intermediate use * Instead of .

#!/bin/bash
phone=phonenum.txt
for ((i=1;i<=5;i++))
do
	# Count the number of lines of file content 
	num=`wc -l phonenum.txt |cut -d' ' -f1`
	# Randomly select one of the rows 
	luck_line=`echo $[$RANDOM%$num+1]`
	# Take out the lucky line 
	luck_person=`head -$luck_line $phone |tail -1`
	# Delete the lucky user in the source file , Avoid secondary extraction 
	sed -i "/$luck_person/d" $phone
	
	echo " The lucky audience is :182****${luck_person:7:4}"
done

3) Batch creation 5 Users , Each user's password is a random number

#!/bin/bash
# Generate a file to save the user name and password  （ Four random numbers ）
echo user{
    1..3}:wang$[$RANDOM%9000+1000] | tr ' ' '\n'>> user_pass.file
# echo user{1..3}:$(pwgen -cn1 12)|tr ' ' '\n'
for ((i=1;i<=5;i++))
do
	user=`head -$i user_pass.file|tail -1|cut -d: -f1`
	pass=`head -$i user_pass.file|tail -1|cut -d: -f2`
	useradd $user
	echo $pass|passwd --stdin $user
done

#!/bin/bash
# Generate a file to save the user name and password  （ Four random numbers ）
echo user{
    1..3}:wang$[$RANDOM%9000+1000] | tr ' ' '\n'>> user_pass.file
# echo user0{1..3}:$(pwgen -cn1 12)|tr ' ' '\n'
for i in `cat user_pass.file`
do
	user=`echo $i|cut -d: -f1`
	pass=`echo $i|cut -d: -f2`
	useradd $user
	echo $pass|passwd --stdin $user
done

3、 ... and . Regular expressions

Regular expressions , Also known as regular expression .（ English ：Regular Expression, In code it is often abbreviated as regex、regexp or RE）, A concept of computer science . Regular expressions are often used for retrieval 、 Replace those that match a pattern ( The rules ) The text of .

Many programming languages support string manipulation with regular expressions . for example , stay Perl A powerful regular expression engine is built in .

The concept of regular expression was originally developed by Unix Tool software in （ for example sed and grep） Popular . Support regular expression programs such as ：find,vim,grep,sed,awk

• For details of regular expressions, you can refer to Novice tutorial
• 70 Collation and summary of regular expressions

Metacharacters	describe	Example
\	Escape character , Escape special characters , Ignore its special significance	a.b matching a.b, But can't match ajb,. Be escaped as a special meaning
^	Match the beginning of the line ,awk in ,^ Is the beginning of the matching string	^tux Match with tux Beginning line
$	Match the end of the line ,awk in ,$ Is the end of the matching string	tux$ Match with tux The line at the end
.	Match break \n Any single character other than	ab. matching abc or bad, Unmatched abcd or abde, Only single characters can be matched
[ ]	Match included in [ character ] Any one of the characters	coo[kl] Can match cook or cool
[^]	matching [^ character ] Any character other than	123[^45] Can't match 1234 or 1235,1236、1237 Fine
[-]	matching [] Any character within the specified range in , Write it in increments	[0-9] Can match 1、2 or 3 Wait for any number
?	Match previous items 1 Time or 0 Time	colou?r Can match color perhaps colour, Can't match colouur
+	Match previous items 1 Times or more	sa-6+ matching sa-6、sa-666, Can't match sa-
*	Match previous items 0 Times or more	co*l matching cl、col、cool、coool etc.
()	Match expression , Create a substring for matching	ma(tri)? matching max or maxtrix
{n}	Match previous items n Time ,n Can be for 0 The positive integer	[0-9]{3} Match any three digits , It can be extended to [0-9][0-9][0-9]
{n,}	Previous items need to match at least n Time	[0-9]{2,} Matching any two or more digits is not supported {n,}{n,}{n,}
{n,m}	Specify that the previous item matches at least n Time , Match at most m Time ,n<=m	[0-9]{2,5} Match any number from two to five digits
|	Alternate matching | Either of the two sides	ab(c|d) matching abc or abd

Four . Add

1.shift

shift： Move the position parameter to the left , Default move 1 position

#!/bin/bash
#  This script can realize   Add the sum of all parameters after the script 
sum=0
while [ $# -ne 0 ]
do
	let sum=$sum+$1
	shift
done
echo sum=$sum

2.expect Auto answer

#!/usr/bin/expect

# Set a variable 
set ip 10.1.1.1
set pass 123456
set timeout 5
#spawn Is to add a shell to the later running process , Used to pass interactive instructions 
spawn ssh root@$ip
#expect It is used to judge whether the last output result in the interaction contains some strings 
expect {
    
	#exp_continue Attach to a expect After the judgment , After matching this item, continue to match other items 
	"yes/no" {
     send "yes\r";exp_continue }
	"password:" {
     send "$pass\r" }
}

expect "#"
#send Used to perform interactive actions , Equivalent to manual input 
send "rm -rf /tmp/*\r"
send "touch /tmp/file{1..3}\r"
send "date\r"
send "exit\r"
expect eof