Hi thundergnat, thanks for your reply. I am indeed (and unfortunately) trying to do this on Windows. Invoking the external program with 'start' seems to mean that Perl doesn't wait for it. I guess this is equivalent to a background command in a Linux shell. The problem is that I need the Perl script to wait for the external command: the user uses that command to scan a document, then the Perl script needs to go on and handle the scanned file. So I cannot see that 'start' helps.