Thank you very much for your reply. My actual command line is:

scp /tmp/data.txt user@123.456.789.24:"C:\\Data\\"
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after password prompt, it worked fine. My first question is: how do I specify windows destination directory? I used:

my $destdir = '"C:\\Data\\"';
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I got the error: scp timed out while trying to connect to "C at ./net_scp.pl line 33 What is the correct directory specification on the windows side? Thanks much.