Shell programming-- case statement and Loop statement (3)
The structure of case multi-branch statement case statement executes different command sequences according to different values of variables.
Example 1 keystroke type recognition prompts the user to enter a character to determine whether the character is a letter, a number or other character #! / bin/bashread-p "Please enter a character:" keycase $key in [Amurz] | [Amurz]) echo "you entered a letter"; [0-9]) echo "you entered a number"; *) echo "you entered a special character" esac
Example 2 enter scores and view grade #! / bin/bashread-p "Please enter your grades:" numcase $num in [8-9] [0-9] | 100) echo "excellent";; 7 [0-9]) echo "good";; 6 [0-9]) echo "qualified";; [0-9] | [1-5] [0-9]) echo "unqualified" *) echo "you typed incorrectly" esac
The structure of the for statement reads different variable values and is used to execute the same set of commands one by one.
Example 1 batch add users store the user name in the name.txt file, and each line has an initial password set to 123456 authentication script
#! / bin/bashTMP=$ (cat / root/name.txt) for USER in $TMPdo echo "user is $USER" useradd $USER echo "123456" | passwd-- stdin $USER > / dev/nulldone
Example 2 according to the IP geological inspection host status IP geology is stored in the demo04.txt file, each line uses the ping command to detect the connectivity of each host
#! / bin/bashIP=$ (cat / root/demo04.txt) for ip in $IPdo ping-c 1-s 1-w 3$ ip > / dev/null if [$?-eq 0] then echo "$ip host exists" else echo "$ip host does not exist" fidone
The structure of the while statement repeatedly tests a condition and executes it repeatedly as long as the condition is true
Example 1 adds a total of 5 users, namely stu1,stu2,stu3..., whose user names start with stu and are numbered in numerical order. The initial passwords are all set to 123456 passwd stdin stu$num & > / dev/null let num++done while [$num-le 5] douseradd stu$num echo "123456"
Example 2 guess the commodity price script through the variable RANDOM to get a random number to prompt the user to guess and record the number of times, and then exit the loop #! / bin/bashrandom=$ (expr $RANDOM% 100) tim=0while truedo read-p "Please enter the price of the commodity:" jia let tim++ if [$jia-eq $random] then echo "Congratulations on guessing" echo "you guessed a total of $tim" exit 0 elif [$jia-lt $random] then echo "your guess is smaller than" else echo "your guess is larger" fidone "
Comprehensive examples enter five stores to buy goods respectively. Finally, check the total consumption #! / bin/bashi=1sum=0while [$I-le 5] do echo "enter the $iStore" read-p "enter (yes/no)" doing while [$doing = "yes"] do echo "1: clothes ¥200" echo "2: shoes ¥100" echo "3: gloves ¥75" echo "4: pants ¥150" read-p "Please select Item sequence to be purchased: "num case $num in 1) echo" clothes purchased successfully "expr $[sum+=200] & > / dev/null ; 2) echo "shoes purchased successfully" expr $[sum+=100] & > / dev/null; 3) echo "Gloves purchased successfully" expr $[sum+=75] & > / dev/null *) echo "trousers purchased successfully" expr $[sum+=150 & > / dev/null esac read-p "whether to continue the purchase (yes/no)" doing done let iTunes + if [$doing = "no"] then continue fidone echo "Total Shopping Price: $sum"
The structure of the until statement repeatedly tests a condition and executes it repeatedly as long as the condition is not true
Example 1 calculates the sum of 1-50 and calculates the sum of 1-50 by cyclic accumulation #! / bin/bashsum=0i=0until [$I-eq 51] do let sum+=$i let i++doneecho "the sum of the total is: $sum"
Example 2 sends an online message for the specified user. If the user is not online (not logged in to the system), try every 5 seconds until the parameter is passed to the script #! / bin/bashif [$#-lt 0] then echo "Usage:$0" exit 1figrep "$1" / etc/passwd & > / dev/nullif [$?-eq 0] Then: else echo "user does not exist" fiuntil who | grep "$1" > / dev/nulldo echo "user is not online" sleep 5doneecho $2 | write $1
Thank you for reading!
