Shell programming syntax and Application

brief introduction

Shell scripts are similar to batch processing under Windows/Dos, that is, they are pre-loaded into a file with various commands to facilitate one-time execution of a program file, mainly for administrator setup or management purposes.However, it is more powerful than batch processing under Windows and more efficient than programs edited with other programs, using commands under Linux/Unix

variable

Variable type Local variable: current user process Environment variables: current user process and subprocess (env/set) Global variable: All user programs can call System variables: built-in bash variables $?: Last command execution returned status; 0 means normal execution, non-0 means abnormal execution $#: Indicates the number of parameters for a script connection $*: Represents all parameters after the script $@: Represents all parameters after the script $0: Name of the running script -: Indicates the position parameter after the script $$: Process number of the current process $!: Last process number to run in the background !$: Parameters that invoke the last command

array

Normal array (integer as subscript) Defined separately: array[0]=v1 array[1]=v2... Continuous definition: array= (var1 var2... Varn) Array=(`cat/etc/passwd`) is separated by spaces View a single element: $ View all elements: $ $ Intercept some elements: $ View number of elements: ${#array[*]} Get the element subscript: ${!array[*]} ${!array[@]} Associated Array (string can be used as subscript, declared in definition first) Definition: declare-A array View associated array declare-A Defined separately: array[a]=v1 array[b]=v2... Continuous definition: array=([name1]=var1 [name2]=var2... [namen]=varn) View individual elements: $ View all elements: $ $ Intercept some elements: $ View number of elements: ${#array[*]} Get the element subscript: ${!array[*]} ${!array[@]} Operation (default 0): let array[name1]++ let array[name1]+=num Empty Array unset array

usage

Magic Bytes (Wildcard)

#!/bin/env bash

View Running Processes

[root@localhost ~]# bash -x my.sh

View process ID

[root@localhost ~]# pgrep process name &>/dev/null

View grammar problems

[root@localhost ~]# bash -n my.sh

date tool

Last minute (day, week, month, year) date -d '-1 minute' The next minute date -d '1 minute' Format date +%d/%b%Y:%H%M

grammar

Invoke a part of a variable

A=123456 echo $=>345

Delete a part of a string

Delete from back to front $

Read variables from files

read -p "Input:" name < filename

Define variable of type, restrict variable

declare [options] variable name = variable value Common Options -i: Declare an integer -r: Declares a readonly variable whose value cannot be changed and cannot be unset -a:Declare an array -x:Declare environment variables

Four operations (integers only)

$((1+1)) $[10-5] Expr 1 + 1 (not exponentially) N=1; let n=n+1; echo $n (variable needs to be defined first)

shift

Move the position parameter left (default 1 bit) or set it to multiple bits

Remove the directory and name of the current file

dirname $A basename $A

shift

#Input parameter one two three four five six #Shift means how many arguments are removed by right shift echo "The script name is ==> $ " echo "Total parameter number is ==> $# " echo "Your whole parameter is ==> '$@' " shift #shift a variable echo "Total parameter number is ==> $# " echo "Your whole parameter is ==> '$@' " shift 3 #A second shift of three variables echo "Total parameter number is ==> $# " echo "Your whole parameter is ==> '$@' "

Variable Content Delete and Replace

url=www.haha.com Get Length: ${$url} Remove a key from left to right: $=>Haha.com Leave left to right to remove as much as possible: $=>com Remove one key from right to left: $=>Www.haha Strip right to left to remove maximum: $=>www

Concurrent Execution

Wrap function body with {} & and add wait keyword

Implement Output

cat << -EOF xx EOF

Random Numbers (0-32767)

$RANDOM Generate random numbers between 0-n-1 $[$RANDOM%n] Generate 10-99 $[$RANDOM%90+10]

Expect (for automatic response)

#Location parameter defines variables set ip xxx set pass xxx #Start a program spawn ssh root@$ip #Capture the appropriate content #Exp_The continue parameter indicates that this capture can be ignored expect { "(yes/no)?" { send "yes\r";exp_continue } "password:" { send "$pass\r";exp_continue } } #Perform operations expect "#" send "rm -rf /tmp/*\r" send "hostname\r" send "date +%F\r" send "touch file\r" send "ls /tmp/\r" expect eof

Conditional Judgment

grammar test condition [Conditions] [[Conditions]] Class C Style Numerical comparison: ((condition)) The difference between [] and []] When determining an empty string, [] needs to add''to the variable; [[]] does not need To separate multiple conditions, [[]] does not need to

Process Control

if structure

grammar if [[ condition1 ]];then command1 elif [[ condition2 ]];then command2 else command3 fi

for structure

grammar With List: for variable in do command done No list (determined by user input, $1): for variable [in "$@"] Class C style: for (( expr1;expr2;expr3 ))

while structure

grammar while expression do command done

until structure

grammar until expression do command done

case statement

grammar case var in pattern 1) command ;; pattern 2) command ;; *)#Equivalent to default command ;; esac

select loop (easy to output menu, infinite loop)

grammar #Define prompt, $PS1,$PS2,$PS3 PS3="Your choice is:" select choice in xxx xxx xxx do case "$choice" in xxx) esac done

function

grammar [function] function name (){ Function Body Print the first parameter passed to the function: echo $1 } call Terminal temporary call:sourceFunction.sh; function_Name Environment variables: function write/etc/bashrc (user in home directory.bashrc) Called in script: function_Name (defined in script |source)Function.sh)

application

Requirements: Randomly generate 1,000 139 phone numbers starting with five lucky viewers

n1=0 n2=0 n3=0 n4=0 n5=0 n6=0 n7=0 n8=0 file=/tmp/phonenum.txt for ((i=1;i<=1000;i++)) do for ((j=1;j<=8;j++)) do let n$j=$[$RANDOM%10] done echo "139$n1$n2$n3$n4$n5$n6$n7$n8" >> $file done

#!/bin/env bash #Draw five lucky viewers phone=/tmp/phonenum.txt for ((i=1;i<=5;i++)) do line=`wc -l $phone|cut -d ' ' -f1` lucky_lines=$[$RANDOM%$line+1] #Take out the number luck_num=`head -$lucky_lines $phone |tail -1` #Replace Display to Screen echo "139****$" echo $luck_num >> /tmp/luck.txt #Delete the extracted number, sed Use double quotes for shell variables sed -i "/$luck_num/d" $phone done

Requirements: Keep logs for the last 3 days

#!/bin/bash #Realization 1: #Periodically delete files in the directory that have been modified for more than 7 days, using absolute paths #Script plus i privileges to prevent misoperation #Method 1: `find /path -mtime +7 -exec rm -r {} \;` #Method 2: `find /path -mtime +7 |xargs rm -rf ` #Realization two: #Keep backup files for the first two working days, using absolute paths #Method 1: `ls -t /path/*.tar.gz | awk 'NR>2' |xargs rm -rf ` #Method 2: `ls -t /path/*.tar.gz|awk 'NR>2 '|bash`

Requirements: Statistics website connection status

#!/bin/bash declare -A state_array states=`ss -ant|grep :80 |cut -d ' ' -f1` for i in $states do let state_array[$i]++ done for j in ${!state_array[*]} do echo $j:$ done

Requirements: Script to view system performance

#!/bin/bash PS3="Your choice is:" #Judgement System os_check(){ if [ -e /etc/redhat-release ];then REDHAT=`cat /etc/redhat-release|cut -d ' ' -f1` else DEBIAN=`cat /etc/issue|cut -d ' ' -f1` fi if [ "$REDHAT" == "Centos" -o "$REDHAT" == "Red" ];then P_M=yum elif [ "$DEBIAN" == "Ubuntu" -o "$DEBIAN" == "ubuntu" ];then P_M=apt-get else echo "Operating system does not support." exit 1 fi } if [ $LOGNAME != root ];then echo "Please use the root account operation." exit 1 fi instll_software(){ if ! which $1 &> /dev/null;then echo $1 "command not found,now the install." sleep 1 os_check $P_M install $2 -y echo "--------------------" fi } while true do select input in cpu_load disk_load disk_use disk_inode mem_use tcp_status cpu_top10 mem_top10 traffic quit do case $input in cpu_load) #CPU utilization and load echo "-------------------------" i=1 while [[ $i -le 3 ]] do #define color echo -e "\033[32m reference value $\033[0m" UTIL=`vmstat|awk ''` USER=`vmstat|awk ''` SYS=`vmstat|awk ''` IOWAIT=`vmstat|awk ''` echo "Util:$UTIL" echo "User use:$USER" echo "System use:$SYS" echo "I/O wait:$IOWAIT" let i++ sleep 1 done echo "-------------------------" break ;; disk_load) #Hard disk I/O load echo "-------------------------" i=1 while [[ $i -le 3 ]] do echo -e "\033[32m reference value $\033[0m" UTIL=`iostat -x -k|awk '/^[v|s]da/'` READ=`iostat -x -k|awk '/^[v|s]da/'` WRITE=`iostat -x -k|awk '/^[v|s]da/'` IOWAIT=`vmstat|awk ''` echo "Util:$UTIL" echo "Read:$READ" echo "Write:$WRITE" echo "I/O wait:$IOWAIT" let i++ sleep 1 done echo "-------------------------" break ;; disk_use) echo "------------------" #Hard Disk Utilization DISK_TOTAL=`fdisk -l|awk '/dev\/sda/&& /^Disk.*byte/'` USE_RATE=`df |awk '/\/dev\/mapper/'` for i in $USE_RATE do flag=`awk -v num1="$i" -v num2=90% 'BEGIN'` if [ $flag -eq 1 ];then PART=`df -h|awk ''` echo "$PART=$%" fi done echo "Disk total:$" echo "Use rate:$" echo "--------------------" break ;; disk_inode) echo "------------------" #Hard disk inode utilization USE_RATE=`df -i |awk '/\/dev\/mapper/'` for i in $USE_RATE do flag=`awk -v num1="$i" -v num2=90% 'BEGIN'` if [ $flag -eq 1 ];then PART=`df -h|awk ''` echo "$PART=$%" else echo "UseRate:"$ echo "Inode use rate no than 90% of the partition." fi done echo "------------------" break ;; mem_use) echo "------------------" MEM_TOTAL=`free -m|awk 'END'` USE=`free -m|awk 'END'` FREE=`free -m|awk 'END'` CACHE=`free -m|awk 'END'` echo "Total:$" echo "Use:$" echo "Free:$" echo "Cache:$" echo "------------------" break ;; tcp_status) #Network Connection Status echo "------------------" COUNT=`ss -ant|awk '!/State/END'` echo "Tcp connect status:\n$COUNT" echo "------------------" break ;; cpu_top10) #Top 10 CPU processes echo "------------------" CPU=`ps -axu|awk ''|sort -k4 -nr|head -10` num=0 for i in $CPU do echo -n "$i" let num++ if [ $num -eq 6 ];then echo let num=0 fi done echo "------------------" break ;; mem_top10) #Top 10 processes in memory usage echo "------------------" MEM=`ps -axu|awk '}'|sort -k4 -nr|head -10` num=0 for i in $MEM do echo -n "$i" let num++ if [ $num -eq 6 ];then echo let num=0 fi done echo "------------------" break ;; traffic) #Network flow while true do read -p "Input network cat name (ens[33/37]):" ens #Judging whether there is if [ `ifconfig |grep -c "\<$ens\>"` -eq 1 ];then break else echo "Input error,please input again." fi done echo "---------------------------" OLD_RX=`ifconfig ens33 |awk ''` OLD_TX=`ifconfig ens33 |awk ''` sleep 1 NEW_RX=`ifconfig ens33 |awk ''` NEW_TX=`ifconfig ens33 |awk ''` IN=`awk 'BEGIN-$))'/1024/1024}'` OUT=`awk 'BEGIN-$))'/1024/1024}'` echo "IN:$MB/s OUT:$MB/s" echo "---------------------------" break ;; quit) exit ;; *) echo "---------------------------" echo "Input number" break echo "---------------------------" ;; esac done done