Gary Yang wrote:
>  Hi,
>   
>  I need to get a random number whenever the perl script is called. Each 
>  time the random number I got should be different.  I use that number to 
>  name generated files, i.e. I want the perl script to generate different 
>  file names whenever it is called. Can someone tell me how to get the 
>  different random number whenever the perl script is called?

A different random number, that is a contradiction:-)

You could start with rand() [ perldoc -f rand ], but you would
still have to check to see if the file existed!

Anothor method is [ perldoc -q temporary ], guides you to File::Temp
but this is mostly intended for temporary files that (in most cases) disappear
when closed.

Depending on you needs, create a filename that is a combination of

	hostname
	clientname
	$^T - secs since epoch	# sorts nicely
	sprintf("%4.4d%2.2d%2.2dT%2.2d%2.2d%2.2d", 1900+$t[5], $t[4]+1,@t[3,2,1,0]);
		where @t = gmtime($^T); # or localtime($^T); # both variants sorts nicely
	$$ - PID
	rand() - a random number <1 

Andn if you need to be _really_ sure:

From  perlopentut :

     And here are things you can do with "sysopen" that you
     cannot do with a regular "open".  As you'll see, it's just a
     matter of controlling the flags in the third argument.

     To open a file for writing, creating a new file which must
     not previously exist:

         sysopen(FH, $path, O_WRONLY | O_EXCL | O_CREAT);

Leading to something like:

	# construct a nice meaningful filename in $path, maybe using the some of the above methods.
..
	use IO::File;
	sysopen(FH, $path , O_WRONLY|O_EXCL|O_CREAT) or die "$0: $path: $!";
	print FH "ok\n";


	where you actually may change the "or die" to a loop:
	$path="foo00";
	until( sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT) ) { $path++; }; print "Got: $path\n";
	But - you end up in a longer and longer loop, and end in trouble if you can't create the fi
le
	for some other reason.

	use strict;
	use warnings;
	use Sys::Hostname;
	use IO::File;

	my $dir="/var/tmp";
	my @ts = gmtime(time()); 
	my $prefix = sprintf("%s-%4.4d%2.2d%2.2dT%2.2d.%2.2d-%d",
				Sys::Hostname::hostname,
				1900+$ts[5], $ts[4]+1, @ts[3,2,1,0],
				$$,
			     );
	my $suffix = 'txt';
	my $maxtry=10;
	my $success=0;
	my $i = 0;
	while ( $i < $maxtry ) {	
	  my $path = sprintf("%s/%s-%d.%s", $dir, $prefix, $i, $suffix);
	  if ( sysopen(FH, $path , O_WRONLY|O_EXCL|O_CREAT)) {
	    $success=1;
	    last;
	  } else {
	    die "$0: $path: $!" unless $! =~ /file exists/i;
	    $i++;
          }
        }
 	die "$0: failed to create unique file - tried $i times" unless $success;

		
	
>  I greatly appreciate your help.
>   
>   
>  Gary
>   
>   
>  
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-- 
print $Std{'Disclaimer'};
$CC =  +-1; # the Computer Constant - very useful when writing loops.    #
$|=printf "Just another [lazy] %s hacker\r",("PERL","perl")[$i+sleep 1]   #
while $i=$i?0:$CC,1;                                                    ###
__EOF__

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