Exercise for Chapter 7 of "Intermediate Perl"

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# Brief: Exercise for Chapter 7 of "Intermediate Perl"

# File: ch7_exam.pl

# Creator: thinkhy

# Date: 12/23/2012

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use File::Find;

use Time::Local;

use File::Spec::Functions 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 * 60;

my($sec, $min, $hour, $day, $mon, $yr, $dow) = localtime;

my $start = timelocal(0, 0, 0, $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_day;

my($gather, $yield) = gather_mtime_between($start, $stop);

find($gather, @starting_directories);

my @files = $yield->( );

for my $file (@files) {

my $mtime = (stat $file)[9]; # 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 = ();

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# 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

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sub {

my $when = (stat $_)[9];

push @files, canonpath( $File::Find::name )

if ($when >= $start_time and $when <= $end_time) },

sub { @files = no_upwards( @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);

}

 

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# 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.

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