Is there a Unix utility to prepend timestamps to lines of text?

Question

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.)

Note on the accepted answer below: strftime() appears to be a GNU awk extension, so if you're on Mac OS, for example, use gawk instead of awk.

Answer 1

How about this?

cat somefile.txt | perl -pne 'print scalar(localtime()), " ";'

Judging from your desire to get live timestamps, maybe you want to do live updating on a log file or something? Maybe

tail -f /path/to/log | perl -pne 'print scalar(localtime()), " ";' > /path/to/log-with-timestamps

Answer 2

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...

Answer 3

I'm not an Unix guy, but I think you can use

gawk '{print strftime("%d/%m/%y",systime()) $0 }' < somefile.txt

Answer 4

Could try using awk:

<command> | awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; }'

You may need to make sure that <command> produces line buffered output, ie it flushes it's output stream after each line; the timestamp awk adds will be the time that the end of the line appeared on its input pipe.

Answer 5

Kieron's answer is the best one so far. If you have problems because the first program is buffering its out you can use the unbuffer program:

unbuffer <command> | awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0; }'

It's installed by default on most linux systems. If you need to build it yourself it is part of the expect package

http://expect.nist.gov

Answer 6

annotate, available via that link or as annotate-output in the Debian devscripts package.

$ echo -e "a\nb\nc" > lines
$ annotate-output cat lines
17:00:47 I: Started cat lines
17:00:47 O: a
17:00:47 O: b
17:00:47 O: c
17:00:47 I: Finished with exitcode 0

Answer 7

Use the read(1) command to read one line at a time from standard input, then output the line prepended with the date in the format of your choosing using date(1).

$ cat timestamp
#!/bin/sh
while read line
do
  echo `date` $line
done
$ cat somefile.txt | ./timestamp

Answer 8

#! /bin/sh
unbuffer "$@" | perl -e '
use Time::HiRes (gettimeofday);
while(<>) {
        ($s,$ms) = gettimeofday();
        print $s . "." . $ms . " " . $_;
}'