10 actual combat and interview common Shell script writing

Matters needing attention

1) Add the interpreter at the beginning: #! /bin/bash

2) Syntax indent, use four Spaces; Add some notes.

3) Naming suggestion rules: variable names in uppercase, local variables in lowercase, function names in lowercase, names reflect the actual effect.

4) The default variable is global. In the function, the variable local is specified as a local variable to avoid contaminating other scopes.

5) There are two commands to help me debug the script: set-e exits the script on non-zero execution, and set-x prints the execution.

6) Scripts must be tested before production.

1 Gets a random string or number

Get a random 8-bit string:

Method 1: # echo $RANDOM | md5sum | cut 1-8471 - c b94f2 method 2: # openssl rand - base64 4 vg3beg = = method 3: # cat /proc/sys/kernel/random/uuid |cut -c 1-8ed9e032cCopy the code

Get random 8-digit numbers:

Method 1: # echo $RANDOM | cksum | cut 1-823648321 - c method 2: # openssl rand - base64 4 | cksum | cut 1-838571131 - c method 3: # date +%N |cut -c 1-869024815Copy the code

Cksum: prints the CRC effect and statistics bytes

Define a color output string function

Function echo_color() {if [$1 == "green"]; Then echo -e "\033[32;40m$2\033[0m" elif [$1 == "red"]; then echo -e "\033[31;40m$2\033[0m" fi} function echo_color() { case $1 in green) echo -e "\033[32;40m$2\033[0m" ;; red) echo -e "\033[31;40m$2\033[0m" ;; *) echo "Example: echo_color red string" esac}Copy the code

The function keyword defines a function, which may or may not be added.

3 Create users in batches

#! /bin/bashDATE=$(date +%F_%T)USER_FILE=user.txtecho_color(){ if [ $1 == "green" ]; then echo -e "\033[32;40m$2\033[0m" elif [ $1 == "red" ]; then echo -e "\033[31; 40m$2\033[0m" fi}# Backup if [-s $USER_FILE];  then mv $USER_FILE ${USER_FILE}-${DATE}.bak echo_color green "$USER_FILE exist, rename ${USER_FILE}-${DATE}.bak"fiecho -e "User\tPassword" >> $USER_FILEecho "----------------" >> $USER_FILEfor USER in  user{1..10}; do if !  id $USER &>/dev/null;  then PASS=$(echo $RANDOM |md5sum |cut -c 1-8) useradd $USER echo $PASS |passwd --stdin $USER &>/dev/null echo -e "$USER\t$PASS" >> $USER_FILE echo "$USER User create successful." else echo_color red "$USER User already exists! " fidoneCopy the code

4 Check whether the software package is installed

#! /bin/bashif rpm -q sysstat &>/dev/null; then echo "sysstat is already installed."else echo "sysstat is not installed!" fiCopy the code

5 Check the service status

#! /bin/bashPORT_C=$(ss -anu |grep -c 123)PS_C=$(ps -ef |grep ntpd |grep -vc grep)if [ $PORT_C -eq 0 -o $PS_C -eq 0 ]; Then the echo "content" | "theme" [email protected] mail - sCopy the code

6 Check the host survival status

Method 1: Put the wrong IP into the array to determine whether the ping failed three times

#! /bin/bash IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"for IP in $IP_LIST; do NUM=1 while [ $NUM -le 3 ]; do if ping -c 1 $IP > /dev/null; then echo "$IP Ping is successful." break else # echo "$IP Ping is failure $NUM" FAIL_COUNT[$NUM]=$IP let NUM++ fi done if [ ${#FAIL_COUNT[*]} -eq 3 ]; then echo "${FAIL_COUNT[1]} Ping is failure!" unset FAIL_COUNT[*] fidoneCopy the code

Method 2: Add the number of errors to the FAIL_COUNT variable to determine whether the ping fails three times

#! /bin/bash IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"for IP in $IP_LIST; do FAIL_COUNT=0 for ((i=1; i<=3; i++)); do if ping -c 1 $IP >/dev/null; then echo "$IP Ping is successful." break else # echo "$IP Ping is failure $i" let FAIL_COUNT++ fi done if [ $FAIL_COUNT  -eq 3 ]; then echo "$IP Ping is failure!" fidoneCopy the code

Method 3: Use the for loop to ping through and then jump out of the loop and continue. If not, the ping will fail to print

#! /bin/bashping_success_status() { if ping -c 1 $IP >/dev/null; $IP Ping is successful." continue fi}IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"for IP in $IP_LIST; do ping_success_status ping_success_status ping_success_status echo "$IP Ping is failure!" doneCopy the code

7 Monitor the CPU, memory, and disk usage

1) the CPU

Analyze CPU statistics with the vmstat tool.

#! /bin/bashDATE=$(date +%F" "%H:%M)IP=$(ifconfig eth0 |awk -F '[ :]+' '/inet addr/{print $4}') # Support only CentOS6MAIL="[email protected]"if! which vmstat &>/dev/null; then echo "vmstat command no found, Please install procps package." exit 1fiUS=$(vmstat |awk 'NR==3{print $13}')SY=$(vmstat |awk 'NR==3{print $14}')IDLE=$(vmstat |awk 'NR==3{print $15}')WAIT=$(vmstat |awk 'NR==3{print $16}')USE=$(($US+$SY))if [ $USE -ge 50 ]; then echo " Date: $DATE Host: $IP Problem: CPU utilization $USE " | mail -s "CPU Monitor" $MAILfiCopy the code

2) memory

#! /bin/bashDATE=$(date +%F" "%H:%M)IP=$(ifconfig eth0 |awk -F '[ :]+' '/inet addr/{print $4}') MAIL="[email protected]"TOTAL=$(free -m |awk '/Mem/{print $2}')USE=$(free -m |awk '/Mem/{print $3 - $6 - $7} ') FREE = $(($TOTAL - $USE)) # memory less than 1 g email alarm if [1024] $FREE - lt; then echo " Date: $DATE Host: $IP Problem: Total=$TOTAL,Use=$USE,Free=$FREE " | mail -s "Memory Monitor" $MAILfiCopy the code

3) the hard disk

#! /bin/bashDATE=$(date +%F" "%H:%M)IP=$(ifconfig eth0 |awk -F '[ :]+' '/inet addr/{print $4}') MAIL="[email protected]"TOTAL=$(fdisk -l |awk -F'[: ]+' 'BEGIN{OFS="="}/^Disk \/dev/{printf "%s=%sG,",$2,$3}')PART_USE=$(df -h |awk 'BEGIN{OFS="="}/^\/dev/{print $1,int($5),$6}')for i in $PART_USE; do PART=$(echo $i |cut -d"=" -f1) USE=$(echo $i |cut -d"=" -f2) MOUNT=$(echo $i |cut -d"=" -f3) if [ $USE -gt 80 ]; then echo " Date: $DATE Host: $IP Total: $TOTAL Problem: $PART=$USE($MOUNT) " | mail -s "Disk Monitor" $MAIL fidoneCopy the code

8 Monitoring disk usage of hosts in batches

Prerequisites The monitoring end and the monitored end do not need to log in to each other using SSH or by key.

Write a configuration file in the format of IP User Port to save SSH connection information of the monitored host

#! /bin/bashHOST_INFO=host.infofor IP in $(awk '/^[^#]/{print $1}' $HOST_INFO); do USER=$(awk -v ip=$IP 'ip==$1{print $2}' $HOST_INFO) PORT=$(awk -v ip=$IP 'ip==$1{print $3}' $HOST_INFO) TMP_FILE=/tmp/disk.tmp ssh -p $PORT $USER@$IP 'df -h' > $TMP_FILE USE_RATE_LIST=$(awk 'BEGIN{OFS="="}/^\/dev/{print $1,int($5)}' $TMP_FILE) for USE_RATE in $USE_RATE_LIST; do PART_NAME=${USE_RATE%=*} USE_RATE=${USE_RATE#*=} if [ $USE_RATE -ge 80 ]; then echo "Warning: $PART_NAME Partition usage $USE_RATE%!" fi donedoneCopy the code

9 Check website availability

1) Check URL availability

Check_url () {HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{HTTP_CODE}" $1) if [$HTTP_CODE -ne 200]; then echo "Warning: $1 Access failure!" Fi} method 2: check_URL () {if! wget -T 10 --tries=1 --spider $1 >/dev/null 2>&1; Echo "Warning: $1 Access failure!" fi}Copy the code

Usage: check_url www.baidu.com

2) Judge URL availability three times

The procedure is the same as the above procedure for checking the host survival status.

Method 1: Use the loop technique, break out of the current loop if successful, otherwise go to the last line #! /bin/bash check_url() { HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $1) if [ $HTTP_CODE -eq 200]; then continue fi}URL_LIST="www.baidu.com www.agasgf.com"for URL in $URL_LIST; do check_url $URL check_url $URL check_url $URL echo "Warning: $URL Access failure!" doneCopy the code

Method 2: Save the number of errors to the variable #! /bin/bash URL_LIST="www.baidu.com www.agasgf.com"for URL in $URL_LIST; do FAIL_COUNT=0 for ((i=1; i<=3; i++)); do HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $URL) if [ $HTTP_CODE -ne 200 ]; then let FAIL_COUNT++ else break fi done if [ $FAIL_COUNT -eq 3 ]; then echo "Warning: $URL Access failure!" fidoneCopy the code

Method 3: Save the error count to array #! /bin/bash URL_LIST="www.baidu.com www.agasgf.com"for URL in $URL_LIST; do NUM=1 while [ $NUM -le 3 ]; do HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $URL) if [ $HTTP_CODE -ne 200 ]; Then FAIL_COUNT[$NUM]=$IP let NUM++ else break fi done if [${#FAIL_COUNT[*]} -eq 3]; then echo "Warning: $URL Access failure!" Unset FAIL_COUNT[*] # Clear array fidoneCopy the code

10 Check the primary/secondary synchronization of MySQL

#! /bin/bash USER=bakPASSWD=123456IO_SQL_STATUS=$(mysql -u$USER -p$PASSWD -e 'show slave status\G' |awk -F: '/Slave_.*_Running/{gsub(": ",":"); Print $0}') #gsub for I in $IO_SQL_STATUS; do THREAD_STATUS_NAME=${i%:*} THREAD_STATUS=${i#*:} if [ "$THREAD_STATUS" != "Yes" ]; then echo "Error: MySQL Master-Slave $THREAD_STATUS_NAME status is $THREAD_STATUS!" fidoneCopy the code

This chapter to write Shell script examples are more practical, in the interview questions also often appear, I hope you refer to more hands-on writing, do not copy and paste to run, this is not to learn!