Shell Programming and Scripting

Instead of using date and awk and cut, I'd just use date and shell built-ins:

Code:

mv file "$(printf 'XYP.ZAT%02d.PGPNX.TRDIY' $((($(date +%Y) + 99) % 100)))"

Note that the code you have will print 1 digit years instead of 2 digit years starting in years 01 through 10 in each century. Note also that date +%y would also work with ksh; but would give you a syntax error in years 08 and 09 in each century if you're using bash.

could plz explain code why u using two ((($(date +%Y) + 99) % 100)))" bracket

I don't know what you mean about using two bracket. There are no brackets; only parentheses. The command I suggested:

Code:

mv file "$(printf 'XYP.ZAT%02d.PGPNX.TRDIY' $((($(date +%Y) + 99) % 100)))"

uses a command substitution inside double quotes using printf to format the name of the destination file operand for the mv command. That accounts for the "$( at the start of that operand and the )" at the end of that operand. The command being run in that command substitution is a printf command with a single quoted format argument of 'XYP.ZAT%02d.PGPNX.TRDIY' where the text other than the %02d is the constant part of the destination filename you specified and the %02d is a format specifier requesting that a decimal value of two or more digits be printed using a leading 0 if the number to be printed is less than 10. The remaining text:

Code:

$((($(date +%Y) + 99) % 100))

is an arithmetic substitution ($(( expression ))) where the expression being processed is:

Code:

($(date +%Y) + 99) % 100

which adds 99 to the result of another command substitution ($(date +%Y) which invokes the date utility to get the complete current year) and then returns the remainder of dividing that sum by 100. That result will be a one or two digit decimal number in the inclusive range 0 through 99 (which will be the last two digits of the previous year).

Note that when I first started trying to come up with a way to do this, I was using %y instead of %Y as the date utility format specifier (which just returns the last two digits of the current year instead of the entire year) so I added 99 instead of subtracting 1 to avoid getting a negative value for the mod operation in cases where the script might be run in a year ending in 00. Since the script is now using %Y, you could get exactly the same results with:

Code:

mv file "$(printf 'XYP.ZAT%02d.PGPNX.TRDIY' $((($(date +%Y) - 1) % 100)))"

if the 99 is confusing you. And if having the parentheses for the various operations next to each other is confusing to you, you can add spaces separating the operators if it makes it easier for you to read:

Code:

mv file "$(printf 'XYP.ZAT%02d.PGPNX.TRDIY' $(( ( $(date +%Y) - 1 ) % 100)) )"