Shell programming case multi-branch statements, loop statements (for, while, etc.), Shell functions, Shell arrays
The structure of case statements:
Execute different command lines for different values of variables
case variable value in pattern 1) Command sequence 1 ;; Mode 2) Command Sequence 2 ;;.....*) Default command sequence esac
Examples:
Character type recognition:
prompting the user to input a character; judging whether the character is a letter, a number or other characters.
The script is as follows:
[root@localhost opt]# vim test01.sh#!/ bin/bashread -p "Please enter a character: " keycase $key in[a-z]|[A-Z]) echo "You entered a letter";;[0-9]) echo "You entered a number";;*) echo "You entered a special symbol"esac execution results as follows: [root@localhost opt]# chmod +x test01.sh [root@localhost opt]# ./ test01.sh Please enter a character: 3 You entered the number [root@localhost opt]# ./ test01.sh Please enter a character: d You entered the letter [root@localhost opt]# ./ test01.sh Please enter a character: #You entered the special symbol [root@localhost opt]#Loop statement for loop statement:
Loop structure: reading different variable values, used to execute the same set of commands one by one.
for variable name in value list do command sequence done
Example 1:
Batch Add Users:
User names are stored in the users.txt file, one per line; initial passwords are set to 123456; authentication scripts.
The specific experiments are as follows:
[root@localhost opt]# tail -5 /etc/passwdavahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologinpostfix:x:89:89::/var/spool/postfix:/sbin/nologintcpdump:x:72:72::/:/sbin/nologinjiang:x:1000:1000:jiang:/home/jiang:/bin/bashapache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin[root@localhost opt]# vim users.txt[root@localhost opt]# cat users.txt zhangsanlisiwangwuzhaoliu[root@localhost opt]# vim test02.sh[root@localhost opt]# cat test02.sh //shell script #!/ bin/bashTMP=$(cat /opt/users.txt)for USER in $TMPdo useradd $USER && echo "123456" | passwd --stdin $USER &> /dev/nulldone[root@localhost opt]# chmod +x test02.sh [root@localhost opt]# ./ test02.sh @localhost opt]# tail -5 /etc/passwdapache:x:48:48:Apache:/usr/share/httpd:/sbin/nologinzhangsan:x:1001:1001::/home/zhangsan:/bin/bashlisi:x:1002:1002::/home/lisi:/bin/bashwangwu:x:1003:1003::/home/wangwu:/bin/bashzhaoliu:x:1004:1004::/home/zhaoliu:/bin/bash[root @localhost opt]# [root@localhost opt]# su zhangsan[zhangsan@localhost opt]$ su lisi Password: [lisi@localhost opt]$
Example 2:
Check host status based on IP address:
IP addresses are stored in the ipadds.txt file, one per line; use ping to check connectivity for each host.
The shell script is as follows:
#!/ bin/bashTMP=$(cat /opt/ipadds.txt)for USER in $TMPdo ping -c 3 -i 0.2 -w 3 $USER &> /dev/null if [ $? -eq 0 ] then echo "$USER is up" else echo "$USER is down" fidonewhile loop statement:
Loop structure: repeatedly test a condition, as long as the condition is repeated execution.
while conditional test operation do command sequence done
Example 1:
Batch Add Users:
User names start with stu and are numbered numerically; add 10 users in total, stu1, stu2,... Stu20; initial password is set to 123456.
The shell script is as follows:
#!/ bin/bashPRE="stu"num=1while [ $num -le 10 ]do useradd $PRE$num echo "123456" | passwd --stdin $PRE$num &> /dev/dull let num++done
Example 2:
Guess the commodity price:
Random numbers are obtained through the variable RANDOM; users are prompted to guess and record the number of times, and exit the loop after guessing.
The shell script is as follows:
#!/ bin/bashTIMES=0PRICE=$(expr $RANDOM % 1000)while truedoread -p "Please guess the price (0-999):" moneylet TIMES++ if [ $money -gt $PRICE ] then echo "Your guess is too big" elif [ $money -lt $PRICE ] then echo "Your guess is too small" else echo "You guessed it correctly, the correct price is: $num" echo "You guessed $TIMES" break fi done until loop statement:
Loop structure: repeatedly test a condition, as long as the condition does not hold, repeated execution.
until conditional test operation do command sequence done
Example 1:
Calculate the sum of 1 - 50:
Calculate the sum of 1 to 50 by cyclic accumulation.
The experiment was as follows:
[root@localhost opt]# vim test04.sh[root@localhost opt]# cat test04.sh #!/ bin/bashi=0sum=0until [ $i -eq 51 ]do let sum+=i let i++doneecho $sum[root@localhost opt]# chmod +x test04.sh [root@localhost opt]# ./ test04.sh 1275[root@localhost opt]#
Example 2:
Send an online message to a specified user:
If the user is not online (not logged in to the system), try every 10 minutes until the user logs in to the system and sends the message; the user name and message are passed to the script through the location parameter.
The script is as follows:
#!/ bin/bashusername=$1#Determine message format if [ $# -lt 1 ];then echo "Usage:`basename $0` []" exit 1fi #Determine if the user exists if grep "^$username:" /etc/passwd > /dev/nullthen :else echo "User does not exist" exit 1fi #Is the user online, if not contact every 5 seconds until who| grep "^$username" > /dev/nulldo echo "User not online" sleep 5donemes=$*echo $mes |write $usernameShell function Shell function definition:
Command sequences are formatted together to facilitate reuse of command sequences.
[ function ] function name (){ command sequence [return x]} //Use return or exit to explicitly end a function calling a method of a function:
Function Name [Parameter 1] [Parameter 2]
Examples:
Sum of two numbers:
Define the function by sum () {}; sum two numbers by calling the function.
The experiment was as follows:
[root@localhost opt]# vim test06.sh [root@localhost opt]# cat test06.sh #!/ bin/bashsum(){ s=`expr $1 + $2` echo $s }[root@localhost opt]# chmod +x test06.sh [root@localhost opt]# ./ test06.sh @localhost opt]# sum 5 611[root@localhost opt]#Shell array application scenarios include: get array length get element length traverse element slice element replace element delete
...... Array Definition Method: Method 1
Array Name = (value0 value1 value2..)
methodology II
Array Name = ([0]=value [1]=value [2]=value...) //Array elements separated by spaces
Method 3 List Name ="value0 value1 value2... ArrayName = ($ListName) Method 4 ArrayName [0]="value" ArrayName [1]="value" ArrayName [2]="value" ArrayIncluded Data Type: Numeric TypeCharacter Type: Use " " or''Definition Get Array Length: Format: ${#ArrayName [@\*]} Instance: [root@localhost ~]# arr_amber =(1 2 3 4 5);[root@localhost ~]#arr_ length=${#arr_ number[*]}[root@localhost ~]# echo $arr length5 Read the assignment of a subscript: Format: ${array name [subscript]} Example: [root@localhost ~]#arr_ index2=${arr_ number[2]}[root@localhost ~]# echo $arr_ index23 Array traversal: [root@localhost ~]# for v in ${arr_ number[@]}> do> echo $V> done12345Shell Script Debugging echo command bash command
Syntax: sh [-nvx] script name
Common options:
-n: Do not execute script, only check syntax. No syntax problems do not display any content, there are problems prompt error. - v: When executing a script, display the script content first, and then execute the script. Give an error prompt when there is an error. - x: Output the executed script content to the screen. set command set -x: turn on adjustment mode set +x: turn off adjustment mode
