L4 Shell

Style Guide

variable name in uppercase
Local variables lowercase
Function names lowercase
Local variables add local

Intro and variable

echo -e enable backslash -n do not output the trailing newline
# 1. comment
:<<EOF
mulit-line 
comment
EOF

${} is refer to variable
$[] is Numeral Calculations
$() is Command substitution

Operator

String

Array

Conditon

[ ] is same as test

Loop

Function

Lib

Demo

• Guessing game

#!/bin/bash
# Guessing game
# 1. generates a random number and guess
answer=$(date +%s%N | cut -c16-17)
count=0
while :
do
    # Note the number of times of selection
    count=$[count+1]
    echo -n "Enter a number between 0 and 99:"
    # 2. Get User Input
    read aNum
    # 3. If so, then exit
    if [ $aNum -eq  $answer ]
    then
        # If you guess right, exit
        echo "Congratulations, you guessed it! You guess $count times"
        break;
        # 4. If the answer is less than or greater than, then prompt 
    elif [ $aNum -lt  $answer ]
    then
        echo "No, more!"
    else
        echo "No, less!"
    fi
done

• Get the current CPU usage

#!/bin/bash
# Get the current CPU usage
cpu_usage_rate(){
    local line=$(cat /proc/stat | grep -B1 -m1  "cpu" | awk '{print $2" "$3" "$4" "$5" "$6" "$7" "$8" "$9}')
    local user=$(echo $line | awk '{print $1}')
    local nice=$(echo $line | awk '{print $2}')
    local system=$(echo $line | awk '{print $3}')
    local idle=$(echo $line | awk '{print $4}')
    local iowait=$(echo $line | awk '{print $5}')
    local irq=$(echo $line | awk '{print $6}')
    local softirq=$(echo $line | awk '{print $7}')
    local steal_time=$(echo $line | awk '{print $8}')
    local guest=$(echo $line | awk '{print $9}')
    local cpu_total=$[user+nice+system+idle+iowait+irq+softirq+steal_time+guest]
    local cpu_used=$[user+nice+system+iowait+irq+softirq+steal_time+guest]
    
    # $[cpu_used/cpu_total] The default is an integer
    # Reserved two precision
    local rate=$(awk 'BEGIN{printf "%.2f\n",'$[cpu_used*100]'/'$cpu_total'}')
    echo "CPU Usage: $rate%"
}

cpu_usage_rate

• Probing the local network

#!/bin/bash

# Detecting an IP address is unobstructed
test_ping(){
    local ip=$1
    if [ -z "$ip" ]
    then
        echo "Parameters can not be empty"
        return
    fi
    
    ping -c1 $ip &>/dev/null
    
    # if [ $? -eq 0 ]
    # then
    #     echo "$ip on"
    # else
    #     echo "$ip off"
    # fi
    [ $? -eq 0 ] && echo "$ip on" || echo "$ip off"
}


for ((i=1; i<255; i++))
do
    test_ping "192.168.31.$i" &
done

# Concurrency
wait
echo "Finished"

• Write log

#!/bin/bash


log_path="./tmp/"
log_file="my.log"
log_fullpath="$log_path$log_file"

# 1. Check log file
check_log(){
    
    # Create file if not exits 
    if [ ! -d $log_path ]; then
        mkdir -p $log_path
    fi
    
    # Create file if not exits 
    if [ ! -f $log_fullpath ]; then
        touch "$log_fullpath"
    fi
    
    # Whether the file is readable
    if [ ! -r $log_fullpath ]; then
        echo "$log_fullpath  文件不可读"
        return 1
    fi
    
    # If the file is writable
    if [ ! -w $log_fullpath ]; then
        echo "$log_fullpath  文件不可写"
        return 1
    fi
    return 0
}

# 2. Backup log
backup_log(){
    # Get File Size
    local size=`ls -l $log_fullpath | awk '{print $5}'`
    if [ $size -gt 1024 ]; then
        local back_file="$log_path`date +'%Y%m%d-%H%M%S'`.log"
        mv -f $log_fullpath $back_file
        echo "Backed up to $back_file"
    fi
    return
}


# 3. Write log file
write_log(){
    check_log
    if [ $? -ne 0 ]; then
        return 1
    fi
    
    backup_log
    local now_time=`date +'%Y-%m-%d %H:%M:%S'`
    echo "[$now_time] $1" | tee -a ${log_fullpath}
    return 0
}

write_log '####################################################'
write_log 'log write testing string 11'
write_log 'log write testing string 22'
write_log '----------------------------------------------------'