Re: [netsaint] System time problem with NetSaint

Hello Amol,

I am sure many people will answer your question but I haven't seen any 
yet, so here goes. Also I hope the list doesn't mind that this post is 
basically all Perl, very little Netsaint!

> Dear Sir, 
> Thx for the solution! 
> But im unable to decipher the command here.. 
> perl -i.bak -pe 's#^\[(\d+)\]#$1 - Your_Time_Correction(eg 2*3600)#e' 
netsaint.log

It's a Perl one-liner script.
-i.bak says edit in place, backing up the original with extension .bak.
-e says the first argument is the actual script to execute, instead of the 
script's name. -p says take in a file (the second argument) line by line, 
putting each line into the default argument $_, execute the script, and 
printout $_. Thus the file (in this case netsaint.log) will have each line 
transformed by the contents of that script, with the original saved as 
netsaint.log.bak. The script itself use the pattern-match-and-substitute 
operator s/// to search for the start of a line (^) immediately followed 
by a literal left bracket (\[) followed by one or more digits (\d+) and a 
right bracket (\]). This is then replaced by $1 - Your_Time_Correction(eg 
2*3600), where $1 is anything matched inside the parenthesis earlier (i.e. 
the digits) and the rest was meant to be replaced by you with your actual 
correction factor. That is, if the error was 2 hours 3 seconds, you'd 
actually put #$1 - 7203#. The 'e' right at the end says the replacement 
string is to be evaluated as an expression, i.e. replace the matched 
pattern with the digits minus the correction factor.

Note there may be a small error here: while the date gets corrected, the 
square brackets will vanish. It might be better to put 
 perl -i.bak -pe 's#^\[(\d+)\]#"[".($1 - 7200)."]"#e' netsaint.log
which should keep the square brackets

> is it necessary that it has to be in multiples of 3600 (1 hr)

No. The time argument is simply seconds. By 'eg 2*3600' he meant put 7200 
if you want 2 hours.

> also pls tell me where this command has to be executed.

If Perl has been set up correctly on your system you should be able to 
execute it from anywhere. Note that if you are not in the directory where 
netsaint.log lives, you will need to give its full path.

> Also, I was unable to find any relations between the 10 digit time 
stamps (eg. 10288....), and the corresponding time value. Please help me 
to know the logic behind the generation of these time stamps. I dont find 
any common link between the sequence of the time stamps. Is it using some 
knind of algorithm?

These time stamps are a standard Unix internal way of representing time, 
commonly known as t_time or epoch time. They represent the number of 
non-leap seconds past midnight, 1st January 1970, UTC (usually as a signed 
32 bit integer) which is roughly how old Unix is. Yes this does mean you 
will need to get a 64 bit machine before the 2038 crisis! This date format 
has many advantages:
- it is constant through out the world, i.e. time zone independent;
- it is very compact (one 32 bit int for seconds, minutes, hours, days, 
months, and years);
- apart from the word size problem in 2038, it runs forever into the past 
and future without any funny glitches or historical weirdness;
- it is very easy to do arithmetic in it, while most other formats are 
horribly confusing; and
- it is very portable.
On the down side, it is hard for humans to read, but while we're talking 
Perl, you can convert epoch dates to human readable format in your own 
timezone, with:

perl -e 'print scalar localtime 1029132827'

(Substituting the number in question for the one I entered.) Similarly if 
you want the current epoch date just go:

perl -e 'print time'

[...]
Stanley wrote:
> perl -i.bak -pe 's#^\[(\d+)\]#$1 - Your_Time_Correction(eg 2*3600)#e' 
netsaint.log 
> 
> may be something like what you want, provided you know that the log 
> entries are __all__ are out by the same constant amount.[...]

Or if there is a time before/after which they are bad by a constant 
amount, you could try something like:

perl -i.bak -pe 's#^\[(\d+)\]#$1<1028132827 ? $1 - 7200 : $1#e' 
netsaint.log 

Substituting the epoch date where it all went wrong for 1028132827 and the 
actual error for 7200. May still be some hand editing at the cross-over 
point if the bad dates went forward in time, though.


Cheers,
Roger

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