LOG-COPY:  Copy part of a log file to a new log file.

Log-copy copies certain records from an existing log file to a new log
file.  This is useful for decimating log files or repairing log files
with junk at the end, such as could arise if a program crashes in the
middle of writing a record.


   log-copy input-log-file range output-log-file [ low[%mod] ]

Records with negative indexes or with indexes in the indicated range
are copied from input-log-file to a newly-created output-log-file.
The range has the usual form of [low][:[high]][%modulus], as described
in parse_range in misc.c.  If high and the colon are omitted, high
defaults to low.  If high is omitted but the colon is present, the
range extends to the end of the file.

If the optional trailing argument is present, the indexes of the
records written (other than those with negative indexes) are changed
so that the first record has index 'low' and subsequent indexes
increase by 'mod'.  The default for 'mod' is the modulus in the input

As a special fudge, an input file range of "-" causes only records
with negative indexes to be copied.

            Copyright (c) 1995 by Radford M. Neal