use Fcntl qw(:seek);

# save STDERR filehandle
open(my $ORIGSTDERR, ">&", STDERR);

# create temporary filehandle to catch STDERR
open(my $CATCHERR, "+>", undef) or die("cannot open temp file :: $!");
open(STDERR, ">&", $CATCHERR); # redirection


## STDERR is captured here ##
open(PIPE, '-|', $somecommand, $arg1, $arg2, $argN, $filename);

...


# restore STDERR filehandle
open(STDERR, ">&", $ORIGSTDERR);

# read captured STDERR from temporary filehandle
seek($CATCHERR, 0, SEEK_SET);
print "From CATCHERR: $_" while <$CATCHERR>;
close($CATCHERR);