[R] Determining which file is newer

Barry Rowlingson b.rowlingson at lancaster.ac.uk
Fri Oct 23 18:14:58 CEST 2009


On Fri, Oct 23, 2009 at 5:02 PM, Dennis Fisher <fisher at plessthan.com> wrote:
> Colleagues,
>
> I wish to execute a task only if a particular file is newer than a second
> file.  I can access the file modification dates using file.info()$mtime.
> This yields a time object (? POSIX).
>                        size    isdir   mode    mtime
>           ctime
>        Testfile        4421    FALSE   755     2009-10-23 08:59:09
>   2009-10-23 08:59:09
> What is the simplest means to compare these two objects?

 Split the string representation of the object into date and time
parts, then split those parts into day, month , year and hour minute
second, taking care of internationalisation and localisation, then
recombine all those parts into a number of seconds since Jan 1 1970,
taking care of leap seconds and the slowing down of the earth due to
the tides of the moon.

 Or just use the usual operators:

 > file.info("/etc/passwd")$mtime <= file.info("/etc/motd")$mtime
[1] TRUE

Barry



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