Shell Programming and Scripting

Hi

I have a shell variable storing DATE in YYYY-MM-DD format
is there a way i extract required field say only DD

Also, would be great if there is a way which could take date format as well so that code is generic for any date format eg DDMMYYYY or DD/MM/YYYY or YYYY/MM/DD etc.

Thanks

What have you tired to accomplish this?

i could achieve doing the same with particular format using "cut" command. was thinking of getting ideas for generic one.

And why you think i didn't try anything before posting here? Can u help?

We think you didn't try anything because you didn't show us that you tried anything. If you show us what you have tried, we can often point out a very minor fix that will make your code work. Why not give us a starting point instead of making us start from scratch? Why not help us help you?

What you want is easy to do it for any given date format. It is not possible to extract DD from MM/DD/YYYY and DD/MM/YYYY or MMDDYYYY and DDMMYYYY and YYYYMMDD and YYYYDDMM since there is no way to determine whether 20122001 was intended to be January 20, 2012 or December 20, 2001 or whether 20140102 was intended to be January 2, 2014 or February 1, 2014.

As long as you have a shell that performs POSIX required parameter expansions, for the formats you specified you could use:

Code:

var="YYYY-MM-DD"
dd=${var##*-}
printf 'var=%s, dd=%s, using %s\n' "$var" "$dd" 'dd=${var##*-}'
var=DDMMYYYY
dd=${var%??????}
printf 'var=%s, dd=%s, using %s\n' "$var" "$dd" 'dd=${var%??????}'
var=DD/MM/YYYY
dd=${var%%/*}
printf 'var=%s, dd=%s, using %s\n' "$var" "$dd" 'dd=${var%%/*}'
var=YYYY/MM/DD
dd=${var##*/}
printf 'var=%s, dd=%s, using %s\n' "$var" "$dd" 'dd=${var##*/}'

which prints:

Code:

var=YYYY-MM-DD, dd=DD, using dd=${var##*-}
var=DDMMYYYY, dd=DD, using dd=${var%??????}
var=DD/MM/YYYY, dd=DD, using dd=${var%%/*}
var=YYYY/MM/DD, dd=DD, using dd=${var##*/}

No, you have a variable storing a STRING that represents a date, using a string of characters that humans have learned to recognize as representative of a date.

To write a generic function, you have to be able to answer this question:

What date is represented by the string '05/04/12'?
Which characters represent the year?
Which characters represent the month?
Which characters represent the day of the month?

Whatever your answer, I can say you are wrong, because it could be just as legitimate to apply some other interpretation.