Shell script programming under Linux 2

1. If you judge some special usage

If [-Z $a] This indicates what happens when the value of variable A is empty

if [!-e file]; Then what happens when the file doesn't exist?

if (($a <1)); Then ... Equivalent to if [$a-lt 1]; Then ... Symbols such as <,>,==,!=,>=,<= cannot be used in []

$ $ does not exist, so n is empty;

[Email protected] ~]# n= ' wc-l/etc/passwd|awk ' {print $} ' [[email protected] ~]# echo $n [[email protected] ~]# if [-Z $n];then echo ' \ $n is null '; Fi$n is null

If Grep-q ' 123 ' 1.txt; Then what happens if the 1.txt contains a ' 123 ' row?

1.txt contains 123;grep-q ' 123 ' 1.txt match OK, the return value is true;

[[email protected] shell]# cat 1.txt123sdwe[[email protected] shell]# if Grep-q "123" 1.txt; then echo Kong;fikong

2. Case Judgment in Shell

Format: case   variable name  in                      value1)                             command                           ;;                       value2)                            command                            ;;                       *)                           commond                             ;;                        esac in a case program, you can use  | in the condition, meaning,  such as 2|3)     command     ;; When the variable is 2 or 3 o'clock, the part of the command is executed.

The /etc/init.d/naginx has a case statement; the first parameter that matches the input is the start stop reload restart Conifgtest, and the other characters are returned

Usage:/etc/init.d/nginx {start|stop|reload|restart|configtest}

Case "$" in start) start;  stop) stop;;  reload) reload;;  restart) restart;;  Configtest) configtest;; *) echo $ "Usage: $ start|stop|reload|restart|configtest}" Retval=1esac

For example, enter a letter, prompt for a pure number, enter a number to determine whether it is even or odd;

[[email protected] 0618]# cat case1.sh #!/bin/bash# requires the number to be entered, to determine odd or even numbers, not to enter a number, and then exit ;read -p  "Please input a number:"  nn1= ' echo  $n |sed  ' s/[0-9]//g ' # The input is a number, the SED is replaced with NULL, the return value is NULL, the return value is not empty;if [ ! -z  the input is a letter $n 1 ]then         echo  "please input a number "     exit  1fin2=$[$n%2]case  $n 2 in   0)     echo  "even"      ;;        1)              echo  "Odd"             ;;        *)              echo  "Not Present"             ;; Esac

[Email protected] 0618]# sh-x case1.sh + read-p ' Please input a number: ' nplease input a number:de2++ echo de2++ sed ' s  /[0-9]//g ' + n1=de+ ' ['! '-Z de '] ' + echo ' please input a number ' please input a number + exit 1[[email protected] 0618]# SH case1.sh Please input a number:234 even [[email protected] 0618]# sh case1.sh Please input a number:weplease input a numbe R

Case Experiment 2: input is blank then prompt to enter a number and then exit, enter the number in 0-100 to determine the score, the input is not a number, then prompted to enter a number and then exit;

Input negative and greater than 100 will prompt for the number of input is 0-100;

#!/bin/bash#case experiment, enter a number for the null prompt to enter the numbers and then exit; The number entered determines the score within 0-100; Enter a number with a non-numeric hint and exit;read -p  "please input  A number: " nif [ -z  $n  ]then        echo   "Please input a number"         exit 1fin1= ' echo  $n |sed  ' s/[-0-9]//g ' #sed替换加了-Indicates negative;if [ ! -z  $n 1 ]then     echo  "please input a number "     exit 1fiif  [  $n  -ge 0 ] && [  $n  -lt 60 ]then         tag=1elif [  $n  -ge 60 ] && [   $n  -lt 80 ]then    tag=2elif [  $n  -ge 80 ]  && [  $n  -lt 90 ]then    tag=3elif [  $n  -ge 90 ] && [  $n  -le 100 ]then    tag=4else     tag=0ficase  $tag  in    1)          echo  "Fail"         ;;         2)                  echo  "Pass"                 ;;               3)                 echo  "Good"                 ;;         4)                 echo  "Excellent"                ;;         *)                 echo  "input number is 0-100"                 ;; Esac

[[Email protected] 0618]# sh case2.sh Please input a number:-200 enter a number for 0-100[[email protected] 0618]# sh case2.sh Put a number:101 the number entered is 0-100

3. Loops in shell scripts

For loop syntax structure: The for variable name in condition; Do ... done

While loop syntax structure: while condition; Do ... done dead loop used: denotes

Break directly ends this layer loop; Continue ignores the code under continue and makes the next loop directly

Exit directly out of the shell

For loop experiment: List all directories in/etc directory

[email protected] ~]# cat for.sh #!/bin/bashfor F in ' ls/etc/' doif [-d/etc/$f]then ls-d "/etc/$f" Fidone

While loop experiment: Judge the load cycle;

[[email protected] ~]# cat load.sh #!/bin/bash# Monitor Load script, take w load value within 1 minutes if greater than 10, then 30 seconds to send mail; while:d oload= ' W |head-1 |awk-f ' lo    Ad average: ' {print $} ' |cut-d.-f1 ' If [$load-gt]then top|mail-s ' load is High: $load ' [Email protected]else Exit 0fi Sleep 30done

While loop experiment:

If the input is empty, the prompt asks to enter something, if the input character prompts to enter a pure number, enter a pure digital printing number, exit;

[[email protected] 0618]# cat while.sh #!/bin/bash# input is empty, prompting you to enter something until the input is not empty, and if you enter a letter, you are prompted to enter only a pure number until you enter a pure number, and the print digit ends; :d o read-p "Please input a number:" N if [-Z $n] then echo "Enter something" Continuefi n1= ' echo $n | Sed ' s/[-0-9]//g ' if [!-Z $n 1] then echo "Please enter a pure number" Continuefi Breakdoneecho $n

Continue exit this cycle, the loop inside continues, does not carry on the back of the loop;

Break jumps out of the loop, and the back of the loop executes.

Exit the word quit the entire script;

Break experiment: Exit the entire loop if conditions match;

[[email protected] 0618]# cat break.sh #!/bin/bash#break experiment; exit the entire loop if the condition matches; the back of the loop executes; for i in ' SEQ 1 5 ' do echo $i I f [$i = = 3]then break Fiecho $idoneecho OK

[Email protected] 0618]# sh break.sh11223ok

Continue experiment; exit this cycle and continue to execute the loop if the conditions match;

#!/bin/bashfor i in ' SEQ 1 5 ' do echo $i if [$i = = 3] Then continue fi echo $idoneecho OK

[Email protected] 0618]# sh continue.sh 112234455OK

Exit experiment; Quit the entire script if the condition matches;

#!/bin/bashfor i in ' SEQ 1 5 ' do echo $i if [$i = = 3] Then Exit 1 fi echo $idoneecho OK

[[Email protected] 0618]# sh break.sh 11223

4. Functions in the shell

The function is to organize a piece of code into a small unit, and give the small unit a name, when the code is used to call the name of the small unit directly.

Format: function F_name () {

Command

}

The function has to be on the front

The function can export global variables;

Function Experiment 1: Define the input function, enter a character, then print a character;

#!/bin/bashinput () {echo $}input yonglinux[[email protected] ~]# sh 1.sh yonglinux

Function Experiment 2: Define the SUM function and perform the sum operation;

#!/bin/bashsum () {s=$[$1+$2] echo $s}sum 1 2[[email protected] 0618]# sh 2.sh 3

View the function of the IP address;

#!/bin/bash# View the function of the IP address, enter a network card name, output the IP address of the network card, the network card name entered for the interaction, IP () {ifconfig |grep-a1 "$" |tail-1|awk ' {print-$} ' |awk-f ' : "{print $} '}read-p" Please input the ETH name: "emyip= ' IP $e ' echo ' $e address is $myip"

[[Email protected] 0618]# sh 2.sh Please input the ETH Name:eth0eth0 address is 192.168.11.100[[email protected] 0618]# sh 2.sh Please input the ETH name:eth1eth1 address is 192.168.20.100[[email protected] 0618]# sh 2.sh Please input the ETH n Ame:lolo address is 127.0.0.1

This article is from the "Model Student's Learning blog" blog, please be sure to keep this source http://8802265.blog.51cto.com/8792265/1664557

Shell script programming under Linux 2