open TEMP,"cleartool checkout -nc $element_pathname 2>&1 |"
    or die "Failed to checkout: $!";
# Read from TEMP as usual, but now we also have STDERR

##</code><code>##

use IPC::Open3;
my $pid = open3 IGNORE,TEMPOUT,TEMPERR,
    'cleartool',"checkout -nc $element_pathname"
    or die "Failed to open3: $!";
# first read from TEMPERR
while (<TEMPERR>) {
    # open3 returns an exec error on the error fh you gave it
    /^open3:/ && die "Error in open3: $_";
    # Check for the cleartool error message here
}
while (<TEMPOUT>) {
    print "The message is - $_";
}
# Don't forget to reap it!
waitpid $pid,0;