Collection of Useful Bash Scripts for Linux Engineers

As a Linux engineer, well‑written scripts can boost productivity and free up time for other tasks; this article gathers a set of useful Bash scripts for common administrative operations.

(1) User Guess Number Game

#!/bin/bash
# Generate a random number between 1 and 100 and let the user guess it
num=$[RANDOM%100+1]
while :
do
  read -p "Computer generated a number between 1‑100, you guess: " cai
  if [ $cai -eq $num ]; then
    echo "Congratulations, you guessed correctly"
    exit
  elif [ $cai -gt $num ]; then
    echo "Oops, too high"
  else
    echo "Oops, too low"
  fi
done

(2) Count Remote IP Connections

#!/bin/bash
# Show how many remote IPs are connected to the host (ssh, web, ftp, etc.)
netstat -atn | awk '{print $5}' | awk '{print $1}' | sort -nr | uniq -c

(3) Hello World Function

#!/bin/bash
function example {
  echo "Hello world!"
}
example

(4) Print Tomcat PID

#!/bin/sh
v1="Hello"
v2="world"
v3=${v1}${v2}
echo $v3
pidlist=`ps -ef|grep apache-tomcat-7.0.75|grep -v "grep"|awk '{print $2}'`
echo $pidlist
echo "tomcat Id list :$pidlist"

(5) Rock‑Paper‑Scissors Game

#!/bin/bash
game=(石头 剪刀 布)
num=$[RANDOM%3]
computer=${game[$sum]}
# ... (rest of the case logic) ...

(6) Multiplication Table (9×9)

#!/bin/bash
for i in `seq 9`
do
  for j in `seq $i`
  do
    echo -n "$j*$i=$[i*j] "
  done
  echo
 done

(7) Install Memcached from Source

#!/bin/bash
# One‑click deployment of memcached
wget http://www.memcached.org/files/memcached-1.5.1.tar.gz
yum -y install gcc
tar -xf memcached-1.5.1.tar.gz
cd memcached-1.5.1
./configure
make
make install

(8) Check if Current User Is Root

#!/bin/bash
if [ $USER == "root" ]; then
  yum -y install vsftpd
else
  echo "You are not an administrator, no permission to install software"
fi

(9) Simple If‑Expression Demo

#!/bin/bash -xv
if [ $1 -eq 2 ]; then
  echo "wo ai wenmin"
elif [ $1 -eq 3 ]; then
  echo "wo ai wenxing"
elif [ $1 -eq 4 ]; then
  echo "wo de xin"
elif [ $1 -eq 5 ]; then
  echo "wo de ai"
fi

(11) Kill and Restart Tomcat Process

#!/bin/bash
pidlist=`ps -ef|grep apache-tomcat-7.0.75|grep -v "grep"|awk '{print $2}'`
echo "tomcat Id list :$pidlist"
kill -9 $pidlist
echo "KILL $pidlist:"
echo "service stop success"
echo "start tomcat"
cd /opt/apache-tomcat-7.0.75
rm -rf work/*
cd bin
./startup.sh

(12) Print Chessboard Pattern

#!/bin/bash
for i in {1..8}
do
  for j in {1..8}
  do
    sum=$[i+j]
    if [ $[sum%2] -eq 0 ]; then
      echo -ne "\033[46m  \033[0m"
    else
      echo -ne "\033[47m  \033[0m"
    fi
  done
  echo
 done

(13) Count Login‑Capable Accounts

#!/bin/bash
# Method 1
grep "bash$" /etc/passwd | wc -l
# Method 2
awk -F: '/bash$/{x++}END{print x}' /etc/passwd

(14) Backup MySQL Table Data

#!/bin/sh
source /etc/profile
dbName=mysql
tableName=db
echo [`date +'%Y-%m-%d %H:%M:%S'`] 'start loading data...'
mysql -uroot -proot -P3306 ${dbName} -e "LOAD DATA LOCAL INFILE '# /home/wenmin/wenxing.txt' INTO TABLE ${tableName} FIELDS TERMINATED BY ';'"
echo [`date +'%Y-%m-%d %H:%M:%S'`] 'end loading data...'
exit

(15) Real‑Time eth0 Packet Flow

#!/bin/bash
while :
 do
  echo 'Local interface ens33 traffic:'
  ifconfig ens33 | grep "RX pack" | awk '{print $5}'
  ifconfig ens33 | grep "TX pack" | awk '{print $5}'
  sleep 1
done

(16) Scan 192.168.4.0/24 Host Status

#!/bin/bash
for i in {1..254}
 do
  ping -c 2 -i 0.3 -W 1 192.168.1.$i &>/dev/null
  if [ $? -eq 0 ]; then
    echo "192.168.1.$i is up"
  else
    echo "192.168.1.$i is down"
  fi
 done

(17) Create User with Password Prompt

#!/bin/bash
read -p "Enter username: " user
if [ -z $user ]; then
  echo "You must enter a username"
  exit 2
fi
stty -echo
read -p "Enter password: " pass
stty echo
pass=${pass:-123456}
useradd "$user"
echo "$pass" | passwd --stdin "$user"

(18) Sort Three Integers

#!/bin/bash
read -p "Enter first integer: " num1
read -p "Enter second integer: " num2
read -p "Enter third integer: " num3
# Simple bubble‑sort logic
if [ $num1 -gt $num2 ]; then tmp=$num1; num1=$num2; num2=$tmp; fi
if [ $num1 -gt $num3 ]; then tmp=$num1; num1=$num3; num3=$tmp; fi
if [ $num2 -gt $num3 ]; then tmp=$num2; num2=$num3; num3=$tmp; fi
echo "Sorted numbers: $num1,$num2,$num3"

(19) Time‑Based Greeting Script

#!/bin/bash
tm=$(date +%H)
if [ $tm -le 12 ]; then
  msg="Good Morning $USER"
elif [ $tm -gt 12 -a $tm -le 18 ]; then
  msg="Good Afternoon $USER"
else
  msg="Good Night $USER"
fi
echo "Current time: $(date +"%Y-%m-%d %H:%M:%S")"
echo -e "\033[34m$msg\033[0m"

(20) Write Text to File

#!/bin/bash
cd /home/wenmin/
touch wenxing.txt
echo "I lov cls" >> wenxing.txt

(21) Simple For‑Loop Summation

#!/bin/bash
s=0
for i in {1..99}
 do
   s=$[s+i]
 done
echo $s

(22) Loop Over Script Arguments

#!/bin/bash
for i in "$*"
 do
   echo "wenmin xihuan $i"
 done
for j in "$@"
 do
   echo "wenmin xihuan $j"
 done

(23) Weekly Log Backup with tar

#!/bin/bash
# Every Friday backup /var/log
tar -czf log-`date +%Y%m%d`.tar.gz /var/log
# Add to crontab: 00 03 * * 5 /home/wenmin/datas/logbak.sh

(24) Sum and Division Functions

#!/bin/bash
function sum {
  s=$[ $1 + $2 ]
  echo $s
}
read -p "input your parameter " p1
read -p "input your parameter " p2
sum $p1 $p2
function multi {
  r=$[ $1 / $2 ]
  echo $r
}
read -p "input your parameter " x1
read -p "input your parameter " x2
multi $x1 $x2
v1=1; v2=2; let v3=$v1+$v2; echo $v3

(25) Case‑Statement Demo

#!/bin/bash
case $1 in
1) echo "wenmin";;
2) echo "wenxing";;
3) echo "wemchang";;
4) echo "yijun";;
5) echo "sinian";;
6) echo "sikeng";;
7) echo "yanna";;
*) echo "danlian";;
esac

(26) Tomcat Monitoring and Auto‑Restart

#!/bin/sh
TomcatID=$(ps -ef|grep tomcat|grep -w 'apache-tomcat-7.0.75'|grep -v 'grep'|awk '{print $2}')
StartTomcat=/opt/apache-tomcat-7.0.75/bin/startup.sh
WebUrl=http://192.168.254.118:8080/
GetPageInfo=/dev/null
TomcatMonitorLog=/tmp/TomcatMonitor.log
Monitor(){
  echo "[info]开始监控tomcat...[$(date +'%F %H:%M:%S')]"
  if [ $TomcatID ]; then
    echo "[info]tomcat进程ID为:$TomcatID."
    TomcatServiceCode=$(curl -s -o $GetPageInfo -m 10 --connect-timeout 10 $WebUrl -w %{http_code})
    if [ $TomcatServiceCode -eq 200 ]; then
      echo "[info]返回码为$TomcatServiceCode, tomcat启动成功, 页面正常."
    else
      echo "[error]访问出错，状态码为$TomcatServiceCode, 错误日志已输出到$GetPageInfo"
      echo "[error]开始重启tomcat"
      kill -9 $TomcatID
      sleep 3
      $StartTomcat
    fi
  else
    echo "[error]进程不存在! tomcat自动重启..."
    echo "[info]$StartTomcat, 请稍候......"
    $StartTomcat
  fi
  echo "------------------------------"
}
Monitor >> $TomcatMonitorLog

(27) Create Linux User with Positional Parameters

#!/bin/bash
useradd "$1"
echo "$2" | passwd --stdin "$1"

(28) Parameter Count and Display

#!/bin/bash
echo "$0 $1 $2 $3"
echo $#
echo $@
echo $*

(29) Memory and Disk Space Alert

#!/bin/bash
disk_size=$(df / | awk '/\//{print $4}')
mem_size=$(free | awk '/Mem/{print $4}')
while :
 do
   if [ $disk_size -le 512000 -a $mem_size -le 1024000 ]; then
     mail -s "Warning" root <
(30) Check File Existence
#!/bin/bash
if [ -f /home/wenmin/datas ]; then
  echo "File exists"
fi
(31) While Loop Summation Example
#!/bin/bash
s=0
i=1
while [ $i -le 100 ]
 do
   s=$[s+i]
   i=$[i+1]
 done
echo $s
echo $i
(32) One‑Click LNMP Deployment (RPM)
#!/bin/bash
# Install LNMP on CentOS/RHEL 7
yum -y install httpd
yum -y install mariadb mariadb-devel mariadb-server
yum -y install php php-mysql
systemctl start httpd mariadb
systemctl enable httpd mariadb
(33) Read Console Parameters with Timeout
#!/bin/bash
read -t 7 -p "input your name " NAME
echo $NAME
read -t 11 -p "input you age " AGE
echo $AGE
read -t 15 -p "input your friend " FRIEND
echo $FRIEND
read -t 16 -p "input your love " LOVE
echo $LOVE
(34) Simple File Copy Wrapper
#!/bin/bash
cp $1 $2
(35) File Existence Test
#!/bin/bash
if [ -f file.txt ]; then
  echo "文件存在"
else
  echo "文件不存在"
fi
The collection demonstrates practical Bash scripting techniques for system monitoring, automation, user management, and service deployment, serving as a handy reference for Linux administrators.