#! /usr/bin/perl

#                    CPIF  --  CoPy IF Different
#
#           usage: cpif source destination
#
#   Cpif is used when updating collections of files, some of which may
#   have been changed, when it is desirable to copy only those files
#   which have actually been modified.  It is, in essence, a local
#   rdist.
#
#   Cpif compares the date of the last modification of the two files
#   and proceeds as follows:
#
#           Source      Destination                Action
#           =======     ===========    ==============================
#            Newer         Older         Copy source to destination.
#            Same          Same          No action; report "files identical".
#            Older         Newer         No action; warning "destination newer."
#

    $from = $ARGV[0];
    $to = $ARGV[1];

    #   Confirm that the input file...

    if (!(-e $from)) {                # exists,
        die("Input file $from does not exist");
    }

    if (!(-f $from)) {                # is a plain data file,
        die("Input file $from is not a plain file");
    }

    if (!(-r $from)) {                # which is readable by me.
        die("Input file $from is not readable");
    }

    #   Okay, now let's obtain the last modification time
    #   for the input and output files.  It's OK if the
    #   output file doesn't exist yet; in that case we
    #   make up a modification time for it one second older
    #   than that of the input file.

    @s = stat($from);
    $fromtime = $s[9];
    if (-f $to) {
        @s = stat($to);
        $totime = $s[9];
    } else {
        $totime = $fromtime - 1;
    }

#$ft = join(":", localtime($fromtime));
#$tt = join(":", localtime($totime));
#print(STDERR "From $from at $ft to $to at $tt.\n");

    #   Now see if the destination needs to be updated.

    if ($totime < $fromtime) {
        $c = "cp -p $from $to\n";
#       print(STDERR "$c");
        system($c);
        print(STDERR "$0: $to updated.\n");
    } elsif ($totime > $fromtime) {
        print(STDERR "$0: source $from older than destination $to.\n");
    } else {
         print(STDERR "$0: source and destination identical.\n");
    }