Universal date functions

Universal date functions-general Linux technology-Linux programming and kernel information. For more information, see the following. #! /Bin/sh

#### Author: RUIFOX
#### Function: Obtain the date before or after any day of a date

#### Parameter 1 is? Get help

If ["$1" = "? "]
Then
Echo "function: get any day before or after a date
Usage: date_g [-B |-a] [n (days)] [Now (yyyymmdd)]
-B indicates the date before.
-A indicates the next date. The default value is-a 1, that is, the next day.
N indicates the number of days in the interval. The default value is 1.
Now indicates the base point date. The default value is the current date.
For example, date_g-a 365 20050210, and the result is 20060210"
Exit
Fi

#### Parameter 2 indicates the number of days separated. The default value is 1 day.
Pre = 1
If ["$2 "! = ""]
Then
Pre = $2
Fi

#### Parameter 3 indicates the base point date. The default value is the current system date.
#### If you want to enter a specific base point Date, parameter 2 cannot be omitted
If ["$3 "! = ""]
Then
Len = 'expr length "$3 "'
If [$ Len! = 8]
Then
Echo "invalid base point Date [$ Len]! "
Exit
Fi
Year = 'echo $3 | awk' {print substr ($, 4 )}''
Month = 'echo $3 | awk' {print substr ($, 2 )}''
Day = 'echo $3 | awk' {print substr ($, 2 )}''
DateP = $3
Else
Month = 'date + % m'
Day = 'date + % d'
Year = 'date + % y'
DateP = 'date + '% Y % m % d''
Fi

#### Parameter 1 indicates counting forward or backward
If ["$1" = "-a"]
Then
Day = 'expr $ day + $ pre'
Ss = ""
Else
Day = 'expr $ day-$ pre'
Ss = "before"
Fi

#### Function mon_max_day to obtain the maximum number of days per month
#### Parameter 1: number of months (1-12)
#### Output: Maximum number of days displayed
Mon_max_day ()
{
Day = 0
If [$1-gt 0-a $1-lt 13]
Then
Case $1 in
1 | 01 | 3 | 03 | 5 | 05 | 7 | 07 | 8 | 08 | 10 | 12) day = 31 ;;
4 | 04 | 6 | 06 | 9 | 09 | 11) day = 30 ;;
2 | 02)
If ['expr $ year % 4'-eq 0]; then
If ['expr $ year % 400 '-eq 0]; then
Day = 29
Elif ['expr $ year % 100 '-eq 0]; then
Day = 28
Else
Day = 29
Fi
Else
Day = 28
Fi ;;
Esac
Fi
Printf $ day
}

#### Start the main program
Max = 'mon _ max_day $ month'

#### Forward
While [$ day-le 0]
Do
Month = 'expr $ month-1'
If [$ month-eq 0]
Then
Month = 12
Year = 'expr $ year-1'
Fi
Max = 'mon _ max_day $ month'
Day = 'expr $ day + $ Max'
Done

#### Backward view
While [$ day-gt $ Max]
Do
Day = 'expr $ day-$ Max'
Month = 'expr $ month + 1'
If [$ month-eq 13]
Then
Month = 1
Year = 'expr $ year + 1'
Fi
Max = 'mon _ max_day $ month'
Done


DateA = 'printf "% 02d % 02d % 02d" $ year $ month $ Day'
# Echo "the date of the base point is [$ DateP], and the date of [$ Pre] day $ Ss is [$ DateA]"
Echo "$ DateA"