If all you need is to capture STDERR as well as STDIN, you ought to be able to use shell redirection:

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
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If you need to be able to distinguish between STDIN and STDERR, your best bet is probably to use IPC::Open3.

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;
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Possibly easier would be using shell redirection to direct each of STDOUT and STDERR into files, and then reading from the files. You might check out perlfaq8 for general info on this stuff, although I couldn't find anything that had a decent open3 example.

echo "Get some open3 examples in the docs\n" | cat >>TODO

-dlc

Translated:

I'm a new user to perl and have recently inherited the role of administrator with the Rational Clearcase confguration control tool (on NT). I'm trying to write simple scripts to import deliveries of software and I am having problems trying to extract error messages after running cleartool commands. The following is an example.

open (TEMP,"cleartool checkout -nc $element_pathname |"),||die "Failed
+ to run cleartool";
while (<\TEMP>){
               print "The message is - $_";
               )
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If the element is not checked out, everythings groovy, I can play with the $_ variable, however if the element is already checked out, the error message is sent to the display, but this appears to be regardless of the print $_ statement, it has not been assigned anything, it doesn't even enter the while loop. This is probabily a simple thing but I'm stumped I need to be able to manipulate this error message. Please Help.
P.S. Any other info would be much appreciated

Quick notes: I hope the comma before the "|| die" and the backslash before the TEMP are typos.