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Full Discussion: Calculate given date - 1 day
Top Forums Shell Programming and Scripting Calculate given date - 1 day Post 302930249 by RavinderSingh13 on Thursday 1st of January 2015 05:08:20 AM
Old 01-01-2015
Quote:
Originally Posted by kmanivan82
Hi Team,
We have a requirement as follows.
If a date 20141220 as parameter to the script, then the script has to return the output as 20141219.
i.e given date - 1.
The requirement is simple. But it should satisfy leap year, the months having 31 and 30 days, the date in which day light savings changes happens, etc,.
The date has to be calculated based on the server date and time.
Can anyone help me out?
Hello kmanivan82,

Pravin's code will work if you have GNU datein your system. Following code may help you to get the previous date of any input date passed by you to script as follows.
Code:
cat date_check.ksh
echo $1 | awk -vs1="01" -vs2="03" -vs3="12" '{if(length($0)>8){print "Wrong Input!!";exit};YEAR=substr($0,1,4);YEAR+0;MONTH=substr($0,5,2);MONTH+0;DATE=substr($0,7,2);DATE+0;split("31 29 31 30 31 30 31 31 30 31 30 31", W," ");if(DATE==s1 && MONTH==s1){YEAR=YEAR-1; MONTH=12; DATE=31; print YEAR MONTH DATE}  else if(DATE==s1 && MONTH >= s1 && MONTH <= s3){MONTH=MONTH-1;W[2]=(YEAR%4!=0)?28:29;print YEAR MONTH W[MONTH]} else {DATE=DATE-1;print YEAR MONTH DATE}}'

Followings are some examples while running the script:
i- simply get previous day
Code:
./date_check.ksh 20201212
20201211   ####### Output

ii- To check about leap year:
Code:
./date_check.ksh 20200301
2020229     ####### Output

iii- To check date of previous month.
Code:
./date_check.ksh 20200401
2020331    ####### Output

This has been made to get the previous date only, kindly check it and let me know if this helps and you have any queries.

EDIT: Adding a non one liner form of code.
Code:
echo $1 | awk -vs1="01" -vs2="03" -vs3="12" '{
                                                if(length($0)>8){
                                                                        print "Wrong Input!!";
                                                                        exit
                                                                }
                                                YEAR=substr($0,1,4);
                                                YEAR+0;
                                                MONTH=substr($0,5,2);
                                                MONTH+0;
                                                DATE=substr($0,7,2);
                                                DATE+0;
                                                split("31 29 31 30 31 30 31 31 30 31 30 31", W," ");
                                                if(DATE==s1 && MONTH==s1){
                                                                                YEAR=YEAR-1;
                                                                                MONTH=12;
                                                                                DATE=31;
                                                                                print YEAR MONTH DATE
                                                                         }
                                                else if(DATE==s1 && MONTH >= s1 && MONTH <= s3){
                                                                                MONTH=MONTH-1;
                                                                                W[2]=(YEAR%4!=0)?28:29;
                                                                                print YEAR MONTH W[MONTH]
                                                                                                }
                                                else {
                                                                                DATE=DATE-1;
                                                                                print YEAR MONTH DATE
                                                     }
                                              }'

Thanks,
R. Singh
Last edited by RavinderSingh13; 01-01-2015 at 06:15 AM.. Reason: Added a non one liner form of code
 

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