$_ = '/////usr///bin///perl////';
s!^/+|/+$!/!g;
print $_, $/;

# but as you can see this is still broken so 
# assuming it is dealing with *nix paths
# you probably want just
$_ = '/////usr///bin///perl////';
s!/+!/!g;
print $_, $/;

# but as tr/// is faster than s/// this will probably be the winner
$_ = '/////usr///bin///perl////';
tr!/!/!s;
print $_, $/;

__DATA__
/usr///bin///perl/
/usr/bin/perl/
/usr/bin/perl/