5-14 Syntax and Parameters
MX2 Reference Guide Revision A MX2A137REFGD
4 - Always overwrite
5 - Overwrite if source is newer
6 - Overwrite if dates or lengths don’t match
7 - Never overwrite
By default, XFER operates in O7 mode—existing files are never
overwritten. For Xmodem, the only valid options are O4 and O7; all
other settings resolve to O7 (never overwrite). All settings for the O
option are available with Zmodem protocol.
To remain compatible with previous versions of XFER, the O option
used without a setting resolves to the O4 setting (always overwrite). This
differs from most other XFER options, where specifying the option
without a setting usually resolves to the default condition for that option.
To use the default condition for the O option, you must specify the O7
setting.
An invalid setting will result in an error on the command line.
Note: XFER does not prompt you to specify whether a file should be
overwritten in the default mode. If no overwrite option is
specified, the file will never be overwritten. Under Xmodem,
the session will abort. Under Zmodem, the file will be skipped
and the next file will be transferred.
For the O6 setting under Zmodem, XFER does not set the date or time of
a received file to match the original date or time of the sender’s version
of the file. Instead, the date and time are taken from the receiver’s
operating system when the file is received and created. Because of this,
it is highly unlikely that a file transferred with XFER will have the exact
date of the original file. Since the resolution of times for files under DOS
is in two-second increments, it is unlikely the timestamps will be the
same, even if the times on the receiver and sender are calibrated
frequently. Also, DOS doesn’t report the seconds field when displaying
the modification time of a file during a file listing. So, two files may
appear to have the same timestamp when in fact they don’t. The
tendency with the O6 option is for files to be overwritten, because times
usually do not match exactly.
The O3 setting is unique in that it causes the transferred file (binary or
ASCII) to be appended to the end of the old file rather than overwriting
it.
With Zmodem, the O option can be used with the C option setting for
crash recovery. If you specify C2 (follow sender) on the command line,
then the receiver will use the sender’s crash and overwrite options. Any
options local to the receiver will be ignored.
