Exercise for Chapter 七 of "Intermediate Perl"

Exercise for Chapter 7 of "Intermediate Perl"

#########################################################################
#  Brief: Exercise for Chapter 7 of "Intermediate Perl"
#  File: ch7_exam.pl
#  Creator: thinkhy
#  Date: 12/23/2012
#########################################################################
use File::use Time::use File::Spec::qw(canonpath no_upwards) 
my $target_dow = 2# Sunday is 0, Monday is 1, ...
my @starting_directories = ".""e:/tmp"my $seconds_per_day = 24 * 60 * 60my$sec$min$hour$day$mon$yr$dow= localtimemy $start = 000$day$mon$yr# midnight today
 
while $dow != $target_dow    # Back up one day
    $start -= $seconds_per_day# hope no DST! :?)
    if --$dow < 0        $dow += 7     
my $stop = $start + $seconds_per_daymy$gather$yield= $start$stop$gather@starting_directories 
my @files = $yield->for my $file @files    my $mtime = stat $file9# mtime via slice
    my $when = localtime $mtime    print "$when: $file\n" 
sub gather_mtime_between     my $start_time = shift    my $end_time = shift 
    my @files =  
    #########################################################################
    # Here use canonpath, details explained as below
    #   canonpath:
    #      No physical check on the filesystem, but a logical cleanup of a path.
    #   no_upwards:
    #     Given a list of file names, strip out those that refer to a 
    #     parent directory. (Does not strip symlinks, 
    #     only '.', '..', and equivalents.)
    # Refer to http://perldoc.perl.org/File/Spec.html
    # 
    # Also, notice that when using stat inside the callback, the filename is $_
    # but when the filename reperting to the user, the name is $File::Find::name
    # because different current working directory for callback and user function
    #########################################################################
    sub           my $when = stat $_9          push @files$File::Find::name           if $when >= $start_time and $when <= $end_time    sub @files = @files         wantarray @files @files  
# Here is the 'official' answer for Chapter 7
sub gather_mtime_between     my$begin$end= @_    my @files 
    my $gatherer = sub         my $timestamp = stat $_9        unless defined $timestamp            warn "Can't stat $File::Find::name: $!, skipping\n"            return                push @files$File::Find::name
        if $timestamp >= $begin and $timestamp <= $end     
    my $fetcher = sub @files     $gatherer$fetcher 
############################################################################
# Compared with answer,  I omitted a special condition that the timestamp 
# will be undef if the stat fails for some reason. That can happen, for example,
# if it finds a dangling symbolic link(the target file doesn't exist).
# In that case, the callback warns the user and returns early. 
# With the code of answer, if we omit that check, we can get warnings of # an undefined value during the comparison with begin time and end time.
############################################################################