How to use the 'date' command to display week number of the year?

The entire format string is to be preceded by the +:

$ date +"So this is week: %U"
So this is week: 19
$ date +"So this is week: %U of %Y"
So this is week: 19 of 2016

There are two kinds of week:

• Monday as first day
• Sunday as first day

So its not all the same when you are in different day of a week(CentOS7):

[[email protected]:~]# date
Mon Aug 26 18:02:47 CST 2019

[[email protected]:~]# date +%U
34

[[email protected]:~]# date +%V
35

date --help
  %U   week number of year, with Sunday as first day of week (00..53)  
  %V   ISO week number, with Monday as first day of week (01..53)

There are actually 3 kind of week number in year for the date command :

• %U week number of year, with Sunday as first day of week (00..53)
• %W week number of year, with Monday as first day of week (00..53)
• %V ISO week number, with Monday as first day of week (01..53)