Man test can see these Comparison symbol:-lt less than-le less than or equal to-gt greater than-ge greater than or equal to-ne does not equal-eq equals < less than (requires double brackets), such as: (("$a" < "$b") <= less than or equal to (requires double brackets), such as: (("$a" <= "$b")) > Greater than (requires double brackets), such as: (("$a" > "$b") >= greater than or equal (requires double brackets), such as: (("$a" >= " $b "))= or = = (requires double brackets), such as: if ["$a" = = "$b"] -b file If the file exists and is a block special file, then true -c file If the file exists and is a character special file, then true -d file If the document exists and is a directory, then true &NBSP;-E File If document exists, then true -f file &nbs P If the file exists and is a rule file, true -g file & nbsp: If the file exists and the Sgid bit value is set, true -h file If the file exists and is A compliance link is true -k file If the file exists and the value of "sticky" bit is set &N Bsp -p file If the file exists and is a named pipe, then true & nbsp &NBSp;-r file If document is present and readable, then true -s file &N Bsp If the file exists and its size is greater than 0, then true -u file &N Bsp If the file exists and the SUID bit is set, true -x file If the file exists and can be True -o file If the file exists and is owned by a valid user ID. -Z string If string length is 0 true -n string If string length is not 0, then true &NBSP;STRING1 = string2 If two strings are equal, true &NBSP;STRING1! = string2 If two strings Not equal, true if then Else statement: if condition 1 then command 1 elif condition 2 &NBSP ; then command 2 else command 3&NBSP;FI complete if and then on the same line that command format is the IF condition 1;then& nbsp;eg:#### #vim name.sh#!/bin/bash#name.shecho-n "Enter you name:" Read Nameif ["$NAME" = = ""]; then echo "Do not enter your name" else echo "you name is: $NAME" fi### #保存退出, chmod +x name.sh### # run./name.sh[[email protected] ~]#./name.sh enter you Name:tony (the name you are typing) you name is:tony Eg:copy a file, if the file does not exist will prompt the system error information, and prompts yourself to give the information # # #vim Ifcp.sh#!/bin/bash#ifcp.shif cp test1.txt MyFile.txt; then echo "Copy is successful" else echo "' basename $ ': NoSuch test1.txt file ">&2fi### #保存退出, chmod +x ifcp.sh### #运行./ifcp.sh -n (-n parameter to check script for syntax errors) [[email Protected] ~]#/ifcp.sh cp:cannot stat ' test1.txt ': No such file or directoryifcp.sh:no such test1.txt File eg : Copy a file, the file does not exist system prompt information does not appear on the screen, display prompts yourself to give the information # # #vim ifcp.sh#!/bin/bash#ifcp.shif CP test1.txt myfile.txt 2>/dev/null ; then echo "Copy is successful" else echo "' basename $ ': No such test1.txt file" >&2fi### #保存 Exit, chmod +x ifcp.sh### #运行./ifcp.sh[[email protected] ~]#./ifcp.sh ifcp.sh:no such test1.txt file Eg:copy a file, the file exists prompts the copy is successful### #vim ifcp.sh#!/bin/bash#ifcp.shif cp 1.txt myfile.txt 2>/dev/null; then echo "Copy is successful" else echo "' basename $ ': No such test1.txt file" fi### #保存退出, chmod +x ifcp.sh### #运行./ifcp.sh[[email protected] ~]#./ifcp.sh copy is successful[[email protected] ~ ]# Cat myfile.txt the End Explanation: ' Bsename $ ' value displays the name of the current script or command, $ displayWill include the path of the current script or command &NBSP;>&2 Redirect to standard error, output to on-screen eg: an If---elif statement---elif--else,- Z Parameters do not know what it means, you can see the man test, note the space and semicolon, quotes # # # #vim ifelse.sh#!/bin/bash#ifelse.shecho-n "Enter Your name:" Read Nameif [-Z $NAME] | | ["$NAME" = ""];then echo "do not enter a NAME" elif ["$NAME" = "root"];then echo "Hello R" Oot "Elif [" $NAME "=" Tony "];then echo" Hello Tony "else echo" Hi, $NAME "fi### #保存退出, chmod +x ifelse . sh### #运行./ifelse.sh[[email protected] ~]#./ifelse.sh enter your Name:roothello root[[email Protected] ~]#./ifelse.sh enter your Name:tonyhello tony[[email protected] ~]#./ifelse.sh enter your Name:jiehi,jie case statement: case value in mode 1) Command 1 ;;Mode 2) Command 2 ;;Esac case The value must be followed by the word in, and each pattern must end with a closing parenthesis. The value can be either a variable or a constant, the matching discovery value conforms to a pattern, and the period all commands begin to execute until;;. Pattern Matching * Denotes any character,? Represents any single character, [...] Represents any character in a class or range eg:##### #vim case.sh#!/bin/bash#case.shecho-n "Enter a number from 1 to 3:" Read anscase $ANS in &N bsp;1) echo "you select 1" ;; 2) echo "you select 2" ;; 3) echo "you select 3" ;; *) echo "' BaseName $ ': This was not between 1 and 3" >&2 exit ;; esac#### #保存退出, chmod + case.sh### #运行./case.sh[[email protected] ~]#./case.sh enter a number from 1 to 3:1you SE Lect 1[[email protected] ~]#./case.sh enter a number from 1 to 3:2you select 2[[email protected] ~]#./cas E.sh enter a number from 1 to 3:3you select 3[[email protected] ~]#./case.sh enter a number from 1 to 3:5c Ase.sh:this is not between 1 and 3 for cycle: for variable name in list do Command 1 Command 2Done When the value of a variable is in the list, the For loop executes all commands once, using the variable name to access the list, the command can be any valid shell command and statement, the variable name is any word, the in list usage is optional, and if not, the For loop uses the command-line positional arguments. The in list can contain replacements, strings, and file names. The argument behind eg:in is a list # # # # # # # # # #vim For1.sh#!/bin/bash#for1.shfor loop in 1 2 3 4 5do echo $loopdone # # # #保存退出, chmod +x for1.sh### #运行./for1.sh[[email protected] ~]#./for1.sh 12345eg:in after the argument is a string # # # # # # # # # #vim for2.sh# For2.shfor loop in "Orange red Bue Grey" do echo $loop "done### #保存退出, chmod +x for2.sh### #运行 ./for2.sh[[email Protected] ~]#./for2.sh orange Red Bue Grey put the contents of the for2.sh for loop in "Orange red Bue Grey" change it to a for loop in orange Red Bue Greyz in the back of the branch shows the argument behind eg:in as a command, "the system command is inside the back quote #vim for3.sh#!/bin/bash#for3.shfor Jie in ' cat MyFile.txt ' do echo $jiedone # # # #保存退出, chmod +x for3.sh [[email protected] ~]# cat Myfile.txt the end[[email protected] ~]#./for3.sh theend eg: A for and if combination of the # # # # #vim For4.sh #!/bin/bash#for4.shecho "Zhe li Mian end you yi ge End"; myfile.txtfor JIE in ' cat myfile.txt ' do If ["$JIE" = "End"];then echo "It is: $JI E " else echo" It is isn't end,it is: $JIE " fidone#### #保存退出, chmod +x For4. sh### #运行./for4.sh[[email protected] ~]#./for4.sh it are not end,it Is:zheit are not end,it is:liit are not end,it Is:mianit Is:endit are not end,it is:youit are not end,it is:yiit are not end,it Is:geit Is:end until cycle: unt Il conditions do Commands 1Command 2 ...The done condition can be any test condition, and the test occurs at the end of the loop, so the loop executes at least once eg: check the size of the disk space, check the disk space every 300s, send the message to the root user ##### the specified number #vim until.sh#!/bin/bash# until.shpart= "/home" look_out= ' df | grep "$Part" | awk ' {print $} ' | Sed ' s/%//g ' echo $LOOK _outuntil ["$LOOK _out"-GT "]do echo" This Filesystem is empty "|mail root look_out= ' df | grep "$Part" | awk ' {print $} ' | Sed ' s/%//g ' Sleep 300done # # # # #保存退出, chmod +x until.sh### #运行./until.sh while loop: while command doCommand 1Command 2 ... Done between while and all usually refers to using a command, but can put a few commands, the command is usually used as a test condition eg:##### #vim while.sh#!/bin/bash#while.shname= name.txtif [ -e "$NAME" ];then echo-e "Zhui jia \ Jin qu \ yi Juhua" >> $NAME &NB Sp else touch $NAME echo-e "Zhe ge Wen jian \ shi xin \ Jian de" ; $NAMEfiwhile Read linedo echo $LINE done < $NAME ##### #保存退出, chmod +x while.sh### #运行. While.shif [ -e "$NAME" &NBSP;] //judge this file has wood, if there will be added a word, no will create a new file, then add a sentence and then through the loop to show him the output, if there is no this file, The first run will only appear echo-e "Zhe ge wen jian \ n shi xin \ Jian de" > $NAME this inside, if run second time, then Echo-e "Zhe ge wen jian \ n Shi xin \ N Jian de "> $NAME will be displayed once, then Echo-e" Zhui Jia \ n jin qu \ yi Juhua ">> $NAME will be entered once, run the third time, echo-e" Zhui Jia \ n ji n qu \ juhua ">> $NAME will show more break control: exit loop if it is in an embedded Ring, you can specify N to jump out of the number of loops, eg:##### #vim BREAK.SH#!/BIN/BASH#BREak.shwhile:d o echo-n "Enter any number [ 1...5]:" read ANS &NB Sp;case $ANS in 1|2|3|4|5) echo "Your Enter a number between 1 and 5." ;; *) echo "wrong number,bye." break ;; esacdone##### #保存退出, chmod +x break.sh### #运行./break.sh[[email protected] ~]#./break.sh enter Any number [ 1...5]:1your Enter a number between 1 and 5.Enter any number [ 1...5]:3your Enter a number BETW Een 1 and 5.Enter any number [ 1...5]:7wrong Number,bye. Explanation: While:, the while is followed by one: indicates that the while statement is always true and jumps out of the loop with a break. continue control: Skip loop step eg:#### #vim breakcontinue.sh #!/bin/bash#break.shwhile:d o echo-n "Enter any number [ 1...5]:" read ANS case $ANS in& nbsp 1|2|3|4|5) echo "Your Enter a number between 1 and 5." ;; *) echo-n "wrong number,continue (y/n?)." Read is_continue case $IS _continue in &N Bsp y|yes| y| Yes) continue; &NBSP ; ;; *) break ;; esac ;; esacdone##### #保存退出, chmod +x breakcontinue.sh #### #运行,./breakcontine.sh[[email protected] ~] #./breakcontinue.sh enter any number [ 1...5]:3your Enter A number between 1 and 5.Enter any number [ 1 ... 5]:7wrong number,continue (y/n?). Yenter any number [ 1...5]:6wrong nUmber,continue (y/n?). N vim Check_server.sh#####!/bin/bashecho "This script would to find which service has started" #to Find www servicetesting= ' Netstat-tlun | grep ":" If [-N "$testing"];then # #if no null is true &NB Sp echo "WWW server has started!" fi #to Find vsftpd servicetesting= ' Netstat-tlun | grep ": +" ' If ["$testing"! = ""];then ## #if no null is true echo " VSFTPD Server has started! " fi #to find ssh servicetesting= ' Netstat-tlun | grep ":" If [-N "$testing"];then echo "SSH server has started!" fi #to Find mail servicetesting= ' Netstat-tlun | grep ":" ' If ["$testing"! = "" ];then echo "MAIL server has started!" Fi ##### function features format: function fname () { program segment}function settings Be sure to have built-in variables at the front of the program, $ 0 indicates the function name, followed by a variable labeled $1,$2,$3.... vim func.sh####!/bin/bashfunction PRIntinfo () { echo "You choice is"}case in "one") Printinfo;echo $ | tr-s ' A-Z ' A-Z ;; "both") Printinfo;echo $ | Tr-s ' A-Z ' A-Z ' ; ESAC #### shell Script Implementation 1+2+...+100vim Sum.sh#####!/bin/bashi=0s=0while ["$i"-lt i=$ (($i + 1)) s=$ (($s + $i)) Doneecho "1+2+3+...+ $i = $s" # # # # # # # # # # # vim sum1.sh#####! /bin/bashs=0for ((i=0;i<=100;i++)) do s=$ (($s + $i)) Doneecho "1+2+". +100= $s another format for "echo" i= $i "#### for vim for.sh#####!/bin/bashfor animal in cat dog pigdo & nbsp Case $animal in "cat") &NB Sp echo "$animal Miao Miao Jiao" &N Bsp ;; "dog") &NBS P echo "$animal Wang Wang Jiao ;; "pig") &NBS P echo "$animal Luo luo jiao" &NBS P ; "*") echo "$animal Jiao Mei Jiao" &N Bsp ; esacdone####
Shell control Flow structure notes
