/sys$common/syshlp/EXCHNGHLP.HLB
COPY, File Qualifiers, /TRUNCATE
 *Conan The Librarian 

       /TRUNCATE
       /NOTRUNCATE

    Controls whether COPY truncates an output file at the end-of-
    file when copying it. The default is /NOTRUNCATE; COPY uses the
    allocation of the input file to determine the size of the output
    file.
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