my $flds = [{ name => UID, start => 0, length => 8 },
            { name => PID, start => 8, length => 6 ),
             # etc. 
             # matches the ps header line in this e.g. 
           ];
my $pid = open my $ph, "ps -ef |" or die $!;
my @hdr = split /\s+/, <$ph>;
while( <$ph> ) {
    my %line;
    for my $fld ( @$flds ) {
        $line{ $fld -> { name } } = substr ( $_, $fld -> { start }, $fld -> { length } );
    }
    # and then match $line{ STIME } against regexps.
}
waitpid $pid, 0;
close $ph