Is there a Unix utility to prepend timestamps to s

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.)

Answer 1

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 2

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 3

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

you can do this (with gnu/sed):

$ some-command | sed "x;s/.*/date +%T/e;G;s/\n/ /g"

example:

$ { echo 'line1'; sleep 2; echo 'line2'; } | sed "x;s/.*/date +%T/e;G;s/\n/ /g"
20:24:22 line1
20:24:24 line2

of course, you can use other options of the program date. just replace date +%T with what you need.

Answer 4

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 5

Could try using awk:

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

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

If awk shows errors, then try gawk instead.

Answer 6

Just gonna throw this out there: there are a pair of utilities in daemontools called tai64n and tai64nlocal that are made for prepending timestamps to log messages.

Example:

cat file | tai64n | tai64nlocal