Singular

datetime() is now part of standard.lib - we will not implement anything
which can be easily done in a library.

For adding your own C/C++ function to Singular
see
[url]http://www.singular.uni-kl.de/DynMod.ps[/url]

Dear Frank,
Pushing date() function into Singular is certainly a good idea. In fact thinking it more generally, and from the prospective feature point of view, will it be possible to "push" any C function through Singular?

I dont know whether how to implement this technically. But sometime I find that some code can be executed with C better that Singular. The workaround for that I do is [code]system ("sh","compile_and_execute_batch_script");[/code]
But then doing this for small code is bit tedious...

-- VInay

There will be a new command in the next minor SINGULAR release called 'datetime' which will return a string of the format

Www Mmm dd hh:mm:ss yyyy

where Www is the weekday, Mmm the month in letters, dd the day of the month as digits, hh:mm:ss the time, and yyyy the year.

I thought it a good idea to have this, as the above proposed workaround is a bit involved, and there actually is a C function which just needed to be pushed through the SINGULAR interpreter...

Usage will be
> datetime;
or
> string s = datetime;

Regards,
Frank

Also this [i]write [/i] command with ">" and ">>" redirections is really a great idea. I had never used/noticed it before! :-)

VInay

Bingo!!! This [i]timestamp() [/i] procedure works perfectly fine... This is what I was looking for!!!

I wonder how come it didnt strike to me to read the file into a string to which I was already writing :-)

Anyways, thanks a lot!

-- VInay

To answer your questions:

1.) The command system returns the errorcode of the shell command,
where 0 means that no error occured. So
[code] write(lnk,system ("sh","date"));[/code]
will only write a 0 to the link.

2.) By construction [b]link[/b]s in Singular bhave very rigid. Once you open
an ascii-file by a link command, you can not acess it simultaneously by [b]>[/b].

Since you only want to write the data to an ASCII file, you have two possibilities.

Either, you don't use [b]link[/b] but access the file simply by its filename
with preceeding > (to open) and >> (to append):

[code]
string lnkname = "file.dat";
write(">"+lnkname,"123"); // creates and write to file.date
write(">>"+lnkname,"hello"); // appends to the file
int errcode = system("sh","date >> " + lnkname); // append the date to file.dat
write(">>"+lnkname,"the end");
read(lnkname); // returns the whole file as a string
[/code]

OR
work constantly work with [b]link[/b] but to get the date as a string,
you have to write it to a file, then read this file into a string,
and finally remove the file to clean the filesystem.

Here is proc which does the job:

[code]
proc timestamp()
{
// returns the date as a string
int errcode;
string fnm = "/tmp/date"+string(system("pid"))+".sig"; // create unique name
errcode = system("sh","date > "+fnm);
string date = read(fnm);
date[size(date)]=""; // remove endining newline
errcode = system("sh","rm -f "+fnm); // remove the date-file
return(date);
}

> timestamp();
Mi 25. Aug 15:21:10 CEST 2010
[/code]

Then you can proceed as expceted:
[code]
link lnk=":a file.txt"; // Note the :a part. The link is appendabble not just writable.
open(lnk);
// do_your_process;
write(lnk,timestamp()); // write the date to the file
// do_remaining_proces;
close(lnk);
[/code]

Essentially the question boils down to:

How to get the output of the following command in string: [code]system("sh","date")[/code]

-- VInay

I want to print the date & time in the output file. I tried various methods. I could get a working solution, but can somebody suggest me a better alternative?
These are the things I have tried:
1.[code] write(lnk,system ("sh","date"));[/code]
Here lnk is a writable link to a text file.
This just prints the output of the system command to the link.

2. Then I tried to write to the file using shell redirections.
[code]write(lnk,system ("sh","date > a"));

OR

write(lnk,system ("sh","date >> a"));[/code]
This really works...

But only if the file is not open! i.e. if the file is opened by some link, then this wont work.

So the only working solution I could find is:
[code]
link lnk=":a file.txt" // Note the :a part. The link should be appendable, not just writable.
open(lnk);
do_your_process;
close(lnk);
write(lnk,system ("sh","date >> a")); // Note the >> redirection. If you put just one > then it will erase the whole
// file and just put the date.
open(lnk);
do_remaining_proces;
close(lnk);
[/code]

Thanks and regards

VInay