The external command entries in the ftpconversions file contain the bulk of the FTP server conversion rules. The external command entry tells the server what should be done with a file after it is transferred to the server. The specified conversion utility can be any command on the server, although generally it is a compression utility. As the file is sent, the server passes the file through the external command. If the file is being uploaded to the server, the command needs to send the result to standard in, whereas a download will send the command to standard out. For example, here is an entry specifying the tar command:
: : :.tar:/bin/tar -c -f - %s:T REG|T DIR:O TAR:TAR
The following sections describe the fields in a conversion entry.
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