Linux operation and Architecture-shell programming (II)

I. Process Control statements

1. If statement

①IF Single branch: one condition one result

If condition  then     command fi

②IF Dual Branch: One condition two results

If condition  then    command Else   command 2fi

③IF Multi-Branch: Multiple conditions multiple results

If condition  then    command elif Condition 2  then    command 2elif condition 3  then    command 3......else   command 4fi

#企业面试题001 #

Development of Detection system memory monitoring script, if less than 800M, mail alarm, and scheduled tasks every three minutes to perform a test

cat check_mem.sh#!/bin/shmem'nr==3{print $NF}'if " $Mem " "  - " ]  then    echo $Mem" system memory less than 800M"774181401@ Qq.comfi

#企业面试题002 #

Simulate the startup Nginx script, using the IF statement to determine if the input is start, stop, restart ...

#!/bin/Sh./etc/init.d/Functionsnginx_start="/application/nginx/sbin/nginx"Nginx_stop="${nginx_start}-S Stop"if[" $"=="Start"] then ${nginx_start} action"starting Nginx"/bin/trueElif [" $"=="Stop"] then ${nginx_stop} pkill Nginx Action"Nginx is stopped"/bin/trueElif [" $"=="Restart"] then ${nginx_stop}&&${nginx_start} action"Nginx is restarting"/bin/trueElif [" $"!="Start"-A" $"!="Stop"-A" $"!="Restart"] Echo"USAGE: $ {Start|stop|restart}"fi

2. Case statement

① syntax

Case $x in value 1)   command 1   ;; Value 2)   command 2   ;; Value 3)   command 3   ;; *)   Command 4esac

The ②case statement is equivalent to a multi-branch if statement, suitable for fewer variables, and a fixed number or set of strings, more for system startup scripts

#case实战菜单小题 #

#!/bin/Bashcat<<EOF1. Install rsync2. Install NFS3. Install MySQL4. Install All5. Exiteofread-P'Please enter your choice:'Num Case$numinch  1) echo"Install rsync suscess!"   ;; 2) echo"Install NFS suscess!"   ;; 3) echo"install MySQL suscess!"   ;; 4) echo"Install all suscess!"   ;; 5) exit;; *) echo"Wrong Choice"Esac

#case结合while实战水果菜单选择 #

#!/bin/ShRED='\e[1;31m'GREEN='\e[1;32m'YELLOW='\e[1;33m'RES='\e[0m'Cat<<EOF==================1. Apple2. Pear3. Banana4. Exit==================EOF while true DoRead-P"Please enter the fruit you like to eat:"Choice Case$choiceinch  1) echo-E"the fruit you like is: $RED Apple $RES"    ;; 2) echo-E"the fruit you like is: $GREEN pear $RES"    ;; 3) echo-E"the fruit you like is: $YELLOW Banana $RES"    ;; 4) exit;; *) echo"wrong input"Esacdone

#给输出字体加颜色 #

Foreground color:
Echo-e "\033[30m black word oldboy trainning \033[0m" echo-e "\033[31m red word oldboy trainning \033[0m" echo-e "\033[32m green word oldboy tr Ainning \033[0m "echo-e" \033[33m yellow word oldboy trainning \033[0m "echo-e" \033[34m blue word oldboy trainning \033[0m "Echo-e" \033[ 35m purple word Oldboy trainning \033[0m "Echo-e" \033[36m sky blue word oldboy trainning \033[0m "echo-e" \033[37m white word oldboy trainning \033[0 M "Background color: echo-e" \033[40;37m Black Bottom White Welcome to old1boy\033[0m "ECHO-E" \033[41;37m Red bottom white Welcome to old2boy\033[0m "ECHO-E" 33[42;37m Green Bottom White Welcome to old3boy\033[0m "ECHO-E" \033[43;37m yellow bottom white Welcome to old4boy\033[0m "ECHO-E" \033[44;37m Blue bottom white wel Come to old5boy\033[0m "echo-e" \033[45;37m purple bottom white Welcome to old6boy\033[0m "Echo-e" \033[46;37m Sky White Welcome to OLD7BOY\03 3[0m "ECHO-E" \033[47;30m black Word Welcome to old8boy\033[0m "Off color \033[0m

3. For statement

① syntax

For i (variable) in {1..10} in the  following can be added command ' ls '  seq ' do     echo $idone

② optimized boot-up via for loop

#!/bin/shclose_service3'{print $}'"crond| Network|sshd|rsyslog|sysstat"' for in $Close _service  Do   chkconfig $name offdone

4. While statement

① syntax

While condition    do command done conditions always set--dead loop daemon: not stopped process true

②while How to read a file by line

mode one,<filesum=0 while the readline does     cmddone mode two , Cat ${file_path}|  while Read Line  Do       cmddone Way three ,while the  readline does       Cmddone <file

③ ways to prevent script interrupts

1, SH while.sh &2, nohup/server/scripts/uptime.sh &3, screen, keep the conversation

5. Functions

① syntax

#!/bin/basholdboy () {    echo "Hello World"}

Note: Oldboy is defined as a function that executes without parentheses, and the function definition and function body must be defined before the name of the function to be executed

function execution method of ② with parameters

Positional parameters in the function body ($, $, $3...$#, $*, and [email protected]) can all be parameters of the function. The parameters of the parent script are temporarily obscured or hidden by the function arguments. $ More special, he is still the name of the parent script. When the function is complete, the original command-line arguments are restored

#!/bin/bashfunction oldboyedu () {echo"Hello World"echo $0echo $1echo $2Exit}etiantian () {echo"Good"    return 3Echo' Bad'} #oldboyedu hanshu1 hanshu2oldboyedu $1$2Etiantian

③ How to write a good function script

#分层 # Each step can be written as a function # each function is split into a function

④ function Advantages

You can reduce the amount of program code by defining the same program segment as a function.
To increase the readability and legibility of the program.
The function of the realization program is modularized.

6. Shell Array

X= (1 2 3) # Print all array contents [[email protected] scripts]# echo ${x[*]}1 2 3# print array elements [[email protected] scripts]# echo ${x[0]}1[[email Protected] scripts]# echo ${x[1]}2[[email protected] scripts]# echo ${x[2]}3# print array length [[email protected] scripts]# echo ${#x [@]} 3[[email protected] scripts]# echo ${#x [*]}3

Second, the individual statement application scenario

if (value judgment)

for (normal loop processing) statements are most commonly used,

while (daemon infinite loop, tasks less than 1 minutes can be used while loop)

Case (System service startup script)

Third, Shell script debugging

① remember to first format the script with Dos2unix.
② directly executes the script according to the error to debug, sometimes inaccurate error.
③sh-x Debug the entire script, showing the execution process.
④set-x and set +x Debug section scripts (set in script)
⑤echo output variables and related content, and then immediately following exit exit, do not execute the way behind the program, step-by-step tracking script, for logic error is better.
Writing: Echo $var; exit
⑥ the most critical is the grammar proficiency, coding habits, programming ideas, to kill the mistakes in the bud, reduce the burden of debugging, improve efficiency

Linux operation and Architecture-shell programming (II)