/usr/bin/perl -w
use strict; 

my $client = 123;  # default value 
my $regx = qr/$client/;
check_logs($regx);

sub check_logs
{
   my $regx = shift(@_);
   my @clients = qw(abc, def, hij);
   foreach my $client (@clients)
      { print($regx, "\n"); } # I want the $regex to bind to the $client variable inside the sub.
}