Is there a Unix utility to prepend timestamps to stdin?

Tags: awk shell unix

I ended up writing a quick little script for this in Python, but I was wondering if there was a utility you could feed text into which would prepend each line with some text -- in my specific case, a timestamp. Ideally, the use would be something like:

cat somefile.txt | prepend-timestamp

(Before you answer sed, I tried this:

cat somefile.txt | sed "s/^/`date`/"

But that only evaluates the date command once when sed is executed, so the same timestamp is incorrectly prepended to each line.)

By : Joe Shaw


Mixing some answers above from natevw and Frank Ch. Eigler.

It has milliseconds, performs better than calling a external date command each time and perl can be found in most of the servers.

tail -f log | perl -pne '
  use Time::HiRes (gettimeofday);
  use POSIX qw(strftime);
  ($s,$ms) = gettimeofday();
  print strftime "%Y-%m-%dT%H:%M:%S+$ms ", gmtime($s);

Alternative version with flush and read in a loop:

tail -f log | perl -pne '
  use Time::HiRes (gettimeofday); use POSIX qw(strftime);
  while(<>) {
    ($s,$ms) = gettimeofday();
    print strftime "%Y-%m-%dT%H:%M:%S+$ms $_", gmtime($s);
By : Keymon

If the value you are prepending is the same on every line, fire up emacs with the file, then:

Ctrl + <space>

at the beginning of the of the file (to mark that spot), then scroll down to the beginning of the last line (Alt + > will go to the end of file... which probably will involve the Shift key too, then Ctrl + a to go to the beginning of that line) and:

Ctrl + x r t

Which is the command to insert at the rectangle you just specified (a rectangle of 0 width).

2008-8-21 6:45PM <enter>

Or whatever you want to prepend... then you will see that text prepended to every line within the 0 width rectangle.

UPDATE: I just realized you don't want the SAME date, so this won't work... though you may be able to do this in emacs with a slightly more complicated custom macro, but still, this kind of rectangle editing is pretty nice to know about...

If you are looking for a Windows console program to do this, I created one here:

By : tim11g

This video can help you solving your question :)
By: admin