Shift dates uniformly in any XML file

date_shift.rb

#!/usr/bin/env ruby
require 'time'

usage = """
Usage: date_shift.rb SECONDS FILE

Look for dates like 2020-06-01T12:26:41Z in FILE
and shift all of them by SECONDS. Print the result to
STDOUT.

E.g. date_shift.rb +100 in.txt > out.txt
"""

unless ARGV.length == 2
  print "Incorrect args!"
  print usage
  exit 1
end

seconds = ARGV[0].to_i
infile = ARGV[1]

input = File.read(infile)

result = input.gsub(/\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z/) do |dateString|
  time = Time.xmlschema(dateString)
    
  (time + seconds).xmlschema()
end

print result