while [ -d /proc/$1 ];do sleep 1;done 

#!/usr/bin/perl
use strict;
use Proc::ProcessTable;

exit if ( $#ARGV == -1 );
$|++;
my $ptable = new Proc::ProcessTable;
my %waited = ();
my %proc;
$proc{ $_->pid }=$_->fname foreach (@{$ptable->table});

use Getopt::Long;

GetOptions(
     'e|exit+'       =>  \( my $endfirst = 0 ),
     's|sleep=i'     =>  \( my $sleeptime = 1 ),
     'v|verbose+'    =>  \( my $verbose = 0),
     'h|help'        =>  sub {
        print "usage: $0 [proces ID|name][...]\n"
          . "\t-s x --sleep x second(S) to sleep between checks\n"
          . "\t-e --exit exit on first terminated process\n"
          . "\t-v --verbose verbose mode\n"
          . "\t-h --help this help\n";
        exit;
});

foreach (@ARGV) {
    next if ( $_ == $$ );    # DON'T wait for myself !
    if (/\d+/) {
        if ( exists $proc{$_} ) {
            $waited{$_}++;
        }
        else { print "nothing like $_\n" if $verbose }
        next;
    }
    foreach my $p ( keys %proc ) {
        next if ( $p == $$ );    # DON'T wait for myself I said !
        $waited{$p}++ if ( $proc{$p} =~ /$_/ );
    }
}

if ($verbose) {
    print "I am process $$\n";
    print "waiting after $_ \n" for ( keys %waited );
    print "sleep time set to $sleeptime s\n";
    print "will exit on first terminated process\n" if ( $endfirst );
}

my $count = scalar keys(%waited);

while ( scalar keys(%waited) ) {
    sleep $sleeptime;
    %proc = ();
    $proc{ $_->pid }++ foreach (@{$ptable->table});
    foreach my $p ( keys %waited ) {
        if ( !exists $proc{$p} ) {
            print "gone $p\n" if $verbose;
            delete $waited{$p};
        }
    }
    last if (( scalar keys(%waited) < $count ) && ($endfirst));
}

__END__

=head1 PSWAIT

pswait  - waiting for process(es) to end before doing things 

=head1 SYNOPSIS
pswait  [options] [process ID|NAME ...]

   Options:
       -h --help            brief help message
       -v --verbose         be verbose
       -e --exit            exit after first process end
       -s x  --sleep x      set sleep time to x second (default to 1)

=head1 OPTIONS

=over 8

=item B<-e, --exit>

When giving a list of process to watch, exit when the first process en
+d, it is usefull to easily manage a pool of proces with a shell scrip
+t.

=item B<-h. --help>

Print a brief help message and exits.

=item B<-s x, --sleep x>

set sleep time to x seconds between process checking, default to 1 sec
+ond. On small machines (or overloaded machines) it could help to chec
+k process state only once every minutes instead, using for example -s
+ 60

=item B<-v, --verbose>

Inform you on what happening ... which process ends, which process ID 
+are watched for state (usefull when using process names on command li
+ne).

=back

=head1 DESCRIPTION

B<pswait> will read the process table of the system
and wait for some process to end 

=head1 AUTHOR

DominiX <dominix@despammed.com> 

=cut
[download]

So as usual, I'll be waiting for your advised recommandations for security, improvement best practice ... and so on, thanks in advance
It looks like there is problem compiling Proc::ProcessTable on Mac Os X . have a look here if interested.
Update 1: more explicit variable name suggested by rob_au
Update 2: use of Getopt::Long and pod formatting as suggested by rob_au and others