Re: date enhancement - filter to preface each line of input with timestamp

[Evan Rempel]

On 11/02/2015 02:25 AM, Pádraig Brady wrote:
> On 01/11/15 22:57, Evan Rempel wrote:
> > There is a lot of discussion on the net about prefacing a timestamp to
> > every line of a text stream. There are solutions with awk, perl, python
> > and bash. coreutils even provides one using perl. This seems to be a
> > very heavy tool to do something that date already does all of the hard
> > work for.
> >
> > Does it make sense to add an option -p --prefix to make date prefix
> > every line of stdin with a date/time stamp?
> It's useful functionality, though already available using other tools.
> http://stackoverflow.com/q/21564/4421
> The general rule we use is to not couple logic
> unless it provides a functional benefit to do so.
> Personally I like the awk solution presented above.
>
> cheers,
> Pádraig.

While I agree in principle with the general rule, I do not agree in this case. All of the solutions I can find on the web, including the one your cite, involve using a different programming language to write a program that solves the problem. In some languages, such as awk, the program is very simple, but it still requires invoking another interpreter to execue a program. Using that logic, there isn't any need for most of the coreutils programs. Just use awk to replace cut or perl to replace tr. 
The coreutils makes this easier to use and easier to read/understand.

Also in this case, the coreutils package includes an application "ts" that is a 
perl script that addresses this exact problem. This implies that at some time in the 
past, coreutils accepted a solution to this problem.

I am proposing that this functionality be moved to the date program to make it less dependent on other system tools. The usual use case for this functionality is for log file generation/piping and ths invocation may be prior to these other tools from being available. It may also be on systems that don't have the required tools or at least where these other tools are not consistently available. The coreutils are as the name implies, core, and as such are more consistently available compared to 
the other more general scripting tools (awk, perl, python).

This feature would arguably make scripts more readable. I would prefer the 
later of these two

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

<command> | date --prefix "+%Y-%m-%d %H:%M:%S"

To understand what the awk solution does, you have to understand awk.

Just for effecientcies sake, timing these two solutions on a 1 million line 
input

awk
1.03user 1.06system 0:02.11elapsed 99%CPU
1.11user 1.04system 0:02.17elapsed 99%CPU
0.97user 1.17system 0:02.17elapsed 99%CPU

date --prefix
0.63user 0.81system 0:01.48elapsed 97%CPU
0.66user 0.80system 0:01.50elapsed 97%CPU
0.62user 0.84system 0:01.50elapsed 97%CPU

Almost 63% more CPU when using awk!

I just wanted to get a feeling for how this feature would be received by the 
coreutils maintainers before I submitted the actual feature request and patch.

Further comments?

--
Evan