Shell Scripting-date comparison and judgment

Compare days with 2 dates

1. Script reference

Script 1:

#!/bin/bash#格式化过期日期，格式化过期日期完整时间以当前时间作为参考！expday="2018-04-11 `date +%T`"echo "Expire day is $expday"#当前日期时间格式为stamp时间戳todays=`date +%s`echo "Today is $(date +"%F %T")"#以下2种方式做时间的四则运算，分别使用 let 或者 $(( ))#过期日期已格式化，规避整数运算的误差（去余数）#let dayDiff=($(date -d "$expday" +%s)-$todays)/86400dayDiff=$(( ($(date -d "$expday" +%s)-$todays)/86400 ))echo "Diff day is $dayDiff days!"

Other Notes:
Bash does not support floating-point operations, and if floating-point operations are required, Bc,awk processing is required.

Script 2:

A method that supports floating-point arithmetic and calculates the exact number of days:

#!/bin/bash#不用刻意格式化过期日，默认时间 00:00:00expday="2018-04-11"echo "Expire day is $expday"todays=`date +%s`echo "Today is $(date +"%F %T")"#仅输出计算公式，管道输出给bc进行浮点运算#scale控制小数位数dayDiff=`echo "scale=2;($(date -d "$expday" +%s)-$todays)/86400"|bc`echo "Diff day is $dayDiff days!"

2. Floating-point comparison method:
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if [ $(echo "1.8 < 15" | bc) = 1 ];thenecho Trueelseecho Falsefi

3. Direct comparison of dates using the date command

3day=$(date -d "$Expday -3 day" %F)2day=$(date -d "$Expday -2 day" %F)

Shell Scripting-date comparison and judgment