What sort of interactive command are you trying to run? (Hint: if it has anything to do with logging into some remote host, that affects what the solution ought to be.)

Is it your intention that the person running the perl script is supposed to type things (after the perl script starts the "interactive command") and these things are then conveyed to (acted on by) the child command process? If so, what sort of value is the perl script supposed to be adding (that is, why use a perl script at all, rather than just running the "interactive command" directly)? If not, just what are you trying to accomplish?

You might need IPC::Open2 (or Open3), or you might need Expect. When you us only vague information, we can only give you back vague advice.

You are presumably trying to do this using `backtics`. Bacticks capture the scripts output into a variable. In fact the "hang" is the program you are running waiting patiently for your input (with the prompt captured by the backtics):

C:\>perl -e "print 'Hello '; system('date'); print 'world'";
Hello The current date is: Tue 17/06/2008
Enter the new date: (dd-mm-yy) 17-06-08
world
C:\>

C:\>perl -e "print 'Hello '; `date`; print 'world'";
Hello 18-06-08  <--- type in data here
world
C:\>date
The current date is: Wed 18/06/2008
[snip]

C:\>perl -e "print 'Hello '; $p = `date`; print $p.' world'";
Hello 17-08-08
The current date is: Tue 17/06/2008
Enter the new date: (dd-mm-yy)  world
C:\>
[download]

#!/usr/bin/perl

# It's only drawback is it only outputs 1 line of bc output
# so it errs on something like 234^12345 (which outputs a big number)

use warnings;
use strict;
use IPC::Open3;
use IO::Select;

#interface to "bc" calculator
my $pid = open3(\*WRITE, \*READ,\*ERROR,"bc");

my $sel = new IO::Select();

$sel->add(\*READ);
$sel->add(\*ERROR);

my($error,$answer)=('','');

while(1){

 print "Enter expression for bc, i.e. 2 + 2\n";
 chomp(my $query = <STDIN>);
 
 #send query to bc
 print WRITE "$query\n";

 foreach my $h ($sel->can_read)
 {
   my $buf = '';
   if ($h eq \*ERROR)
   {
     sysread(ERROR,$buf,4096);
     if($buf){print "ERROR-> $buf\n"}
   }
   else
   {
     sysread(READ,$buf,4096);
     if($buf){print "$query = $buf\n"}
   }
 }
}

waitpid($pid, 1);
# It is important to waitpid on your child process,  
# otherwise zombies could be created.
[download]

#!/usr/bin/perl 
use warnings;
use strict;

print "Enter a search pattern.\n";
my $info=<STDIN>;
chomp($info);
if ( $info =~ m/\w+/ ) {
    system("dir $info");
}
else {
    print "You didn\'t enter text.\n";
}
[download]

C:\Info>perl search.pl
Enter a search pattern.
why*
 Volume in drive C has no label.
 Volume Serial Number is ACCF-791E

 Directory of C:\Info

02/25/2008  07:40 PM               175 whydont.pl
               1 File(s)            175 bytes
               0 Dir(s)  51,114,610,688 bytes free
[download]