Comparing and transforming a date that is piped to (probably) awk? - shell

Question

I've got a reasonably complicated string of piped shell commands (let's assume it's bunch | of | commands), which together produces several rows of output, in this format:
some_path/some_file.csv 1439934121
...where 1439934121 is the file's last-modified timestamp.
What I need to do is see if it's a timestamp on the current day, i.e. on or after last midnight, and then include just the lines where that is true.
I assume this means that some string (e.g. the word true) should either replace or be appended to the timestamps of those lines for grep to distinguish them from ones where the timestamps are those of an earlier date.
To put it in shell command terms:
bunch | of | commands | ????
...should produce:
some_path/some_file.csv true or some_path/some_file.csv 1439934121 true
...for which I could easily grep (obviously assuming that last midnight <= 1439934121 <= current time).
What kind of ???? would do this? I'm almost certain that awk can do what I need it to, so I've looked at it and date, but I'm basically doing awk-by-google with no skills and getting nowhere.
Don't feel constrained by my tool assumptions; if you can achieve this with alternate means, given the output of bunch | of | commands but still using shell tools and piping, I'm all ears. I'd like to avoid temp files or Perl, if possible :-)
I'm using gawk + bash 4.3 on Ubuntu Linux, specifically, and have no portability concerns.

Answer 1

Since today 00:00:00 with the %s format returns the unix timestamp of that moment:
$ date -d'today 00:00:00'
Thu Sep 3 00:00:00 CEST 2015
$ date -d 'today 00:00:00' "+%s"
1441231200
You can probably pipe to an awk doing something like:
... | awk -v midnight="$(date -d 'today 00:00:00' '+%s')" '{$2= ($2>midnight) ? "true" : "false"}1'
That is, use the ternary operator to check the value of $2 and replace with either of the values true/false depending on the result:
awk -v midnight="$(date ...)" '{$2= ($2>midnight) ? "true" : "false"}1'
Test
$ cat a
hello 1441231201
bye 23
$ awk -v midnight="$(date -d 'today 00:00:00' '+%s')" '{$2= ($2>midnight) ? "true" : "false"}1' a
hello true
bye false