String concatenation

Try this:

appendf("err_%02d_count", x);

 Thanx Stephen, But I want to replace '%02d' with a variable : i.e.  '%xd' which is not possible

Have you read the manual to see the syntax of appendf()?
If you want the number in hex, then modify my suggestion to use the %x print format instead of %d.

The arguments for appendf() are exactly like the printf() function in C, so it should be pretty obvious how to adapt it for your needs...

 Stephen, What I meant was I want to replace with a 02 with loop variable x or y .,say(e.g. with y )  err_%yd_cnt which is not possible....!!!!

Please don't keep saying it's not possible, you just need to understand what the C printf() format string means.
A quick Google search or looking at a C text book will tell you all you need.

In order to help you, I have written a small demo. Here is the Specman code:

$ cat print_demo.e
<'
extend sys {
  run() is also {
    for x from 0 to 5 {
      out( appendf("err_%02d_count", x) );
    };
  };
};
'>

And here is the output from the demo code:

$ specman -c "load print_demo ; test"
Welcome to Specman Elite (08.20.003-s)  -  Linked on Thu Mar  5 17:31:56 2009

Protected by U.S. Patents 6,141,630 ;6,182,258; 6,219,809; 6,347,388;
6,487,704; 6,499,132; 6,502,232; 6,519,727; 6,530,054; 6,675,138; 6,684,359;
6,687,662; 6,907,599; 6,918,076; 6,920,583; Other Patents Pending.

Checking license ... OK
Loading print_demo.e ...
read...parse...update...patch...h code...code...clean...
Doing setup ...
Generating the test using seed 1...

Starting the test ...
Running the test ...
err_00_count
err_01_count
err_02_count
err_03_count
err_04_count
err_05_count
No actual running requested.
Checking the test ...
Checking is complete - 0 DUT errors, 0 DUT warnings.

 ThanxStephen.. misinterpretation from my side.....

Also, I saved the above appendf o/p to a variable(loop_str) (of type string ). My requirement was to access an hdl signals with the name err_<number>_count put inside the loop. But when I try to access using the stored variable(loop_str); error meessage pops up saying hdl signal loop_str doesn't exist in the hdl sig def.   i.e. it doesn't take the replacement for loop_str. Is there any way in which this can be done?

I see...

If your ports are declared as a list, you're in luck, but if you copied & pasted 100 instances of the port, you're pretty much stuck.

Loop example:

err_count[100] : list of in simple_port of bit is instance;

keep for each in err_count { it.hdl_path() == appendf("err_%02d_count", index); };

That should give you a feel for what to try or look up in the docs :-)
Good luck!