Ruby RegEx used to search and replace

Question

I have a file with rows of an SQL dump. It has dates in the format yyyy-mm-dd (eg. 2012-08-13 )

I'd like to replace all those dates with a marker so that in the future I can populate the database with rows that are all centered around the date at the time.

For example

• 2012-08-13 I want to change to be stored as something like $$MAINDATE$$
• 2012-08-14 I want to be $$MAINDATE+1$$

This way they are all stored relative to a single date and the data will make sense backwards and forwards off the new creation date.

Then I'd like to iterate the file and replace them all with a new date based on an argument at the time. And adjusted dates based on the +1 or +100 or however many days away it will be at the end.

I think the match text is /\\d{4}-\\d{2}-\\d{2}/

But how do I replace the text that is matched with a new term taking up and replacing the old text?

Update:

I used this to change the markers back to dates.. I doubt its pretty but its working

#iterate each line and look for the marker
while (line = infile.gets)
 str = line
#replace marker with data modified by the modifier
rules = Hash[str.scan(/(\$\$MAINDATE(\+|\-)\d{1,5}\$\$)/).uniq.collect do |e| 
    modifyValue = e[0].split(e[1])[1].gsub("$","").to_i
    if e[1] == "-" then
        modifyValue = modifyValue * -1 
    end
    [e[0], (today + modifyValue).to_s] 
end    ]
  rules.each do |key, value|
    str.gsub!(key, value)
  end
#write new line to array
finishedText.push str
end

Answer 1

Something like this:

require 'date'
def munge_dates list, base_date = Date.today
  date_regexp = /\d{4}-\d{2}-\d{2}/
  list.map do |line|
    days_difference = "%+d" % (Date.parse(line[date_regexp]) - base_date)
    line.sub date_regexp,"$$MAINDATE#{days_difference}$$"
  end
end

If you don't want a $$MAINDATE+0$$ in there then some conditional logic would need to be added.

Answer 2

require "date"

def format_log(str, marker, refdate)
  rules = Hash[str.scan(/\d{4}-\d{2}-\d{2}/m).uniq.collect{|e| [e, (Date.parse(e)-refdate).to_i]}]
  rules.each do |key, value|
    replacement =  "%s%s" % [value >= 0 ? "+" : "", value]
    str.gsub!(key, marker % replacement )
  end
  str
end

p format_log("2012-08-13\n2012-08-14\n2012-08-12", "$$MAINDATE%s$$", Date.today)

will output

"$$MAINDATE+0$$\n$$MAINDATE+1$$\n$$MAINDATE-1$$"