Re: perl; Trying to get File::stat to work

[David Christensen <dpchrist@holgerdanske.com>]

On 10/19/18 7:47 PM, Martin McCormick wrote:
> #!/usr/bin/perl -w
> use strict;
> use warnings::unused;
> use File::stat;
> use File::Spec;
>
> my $last_update_time;
>
> $last_update_time = ( stat("testfile") )[9];
> printf("%d\n",$last_update_time);

My system:

2018-10-20 20:59:53 dpchrist@vstretch ~/sandbox/perl
$ cat /etc/debian_version
9.5

2018-10-20 21:00:10 dpchrist@vstretch ~/sandbox/perl
$ perl -v

This is perl 5, version 24, subversion 1 (v5.24.1) built for 
x86_64-linux-gnu-thread-multi
(with 81 registered patches, see perl -V for more detail)

Copyright 1987-2017, Larry Wall

Perl may be copied only under the terms of either the Artistic License 
or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl".  If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.


Create a test file:

2018-10-20 20:59:22 dpchrist@vstretch ~/sandbox/perl
$ touch testfile


Your program:

2018-10-20 20:57:38 dpchrist@vstretch ~/sandbox/perl
$ vi File-stat.pl

#!/usr/bin/perl -w
use strict;
use warnings::unused;
use File::stat;
use File::Spec;

my $last_update_time;

$last_update_time = ( stat("testfile") )[9];
printf("%d\n",$last_update_time);


Compile it:

2018-10-20 21:00:26 dpchrist@vstretch ~/sandbox/perl
$ perl -c File-stat.pl
Can't locate warnings/unused.pm in @INC (you may need to install the 
warnings::unused module) (@INC contains: 
/home/dpchrist/perl5/lib/perl5/5.24.1/x86_64-linux-gnu-thread-multi 
/home/dpchrist/perl5/lib/perl5/5.24.1 
/home/dpchrist/perl5/lib/perl5/x86_64-linux-gnu-thread-multi 
/home/dpchrist/perl5/lib/perl5 /etc/perl 
/usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 
/usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 
/usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 
/usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base) at 
File-stat.pl line 3.
BEGIN failed--compilation aborted at File-stat.pl line 3.


The Perl binary is installed in different locations on different 
systems.  Revise shebang line to something that is supposed to be more 
portable.


Leave off '-w' option on shebang line.  'use warnings' normally:


2018-10-20 21:00:57 dpchrist@vstretch ~/sandbox/perl
$ vi File-stat.pl

#!/usr/bin/env perl
use strict;
#use warnings::unused;
use warnings;
use File::stat;
use File::Spec;

my $last_update_time;

$last_update_time = ( stat("testfile") )[9];
printf("%d\n",$last_update_time);


Compile:

2018-10-20 21:01:48 dpchrist@vstretch ~/sandbox/perl
$ perl -c File-stat.pl
File-stat.pl syntax OK


Run:

2018-10-20 21:01:58 dpchrist@vstretch ~/sandbox/perl
$ perl File-stat.pl
Use of uninitialized value $last_update_time in printf at File-stat.pl 
line 11.
0


So, the error is reproducible.


RFTM File::stat.  Note that File::stat overloads Perl's core stat() 
function (becomes File::stat object constructor).  'stat' now returns an 
object, not a list.


Use Data::Dumper to see what's going on.


File::Spec is unused -- comment it out.


Use object-oriented attribute accessor method 'mtime' to obtain file 
modification time.


2018-10-20 21:04:58 dpchrist@vstretch ~/sandbox/perl
$ vi File-stat.pl

#!/usr/bin/env perl
use strict;
#use warnings::unused;
use warnings;
use Data::Dumper;
use File::stat;
#use File::Spec;

# my $last_update_time;

#$last_update_time = ( stat("testfile") )[9];
#printf("%d\n",$last_update_time);

my $f = "testfile";

my $st = stat($f) or die "File::stat constructor failed: $!";
print Data::Dumper->Dump([$st], [qw(st)]);

printf("%d\n", $st->mtime);

2018-10-20 21:16:11 dpchrist@vstretch ~/sandbox/perl
$ perl -c File-stat.pl
File-stat.pl syntax OK

2018-10-20 21:17:22 dpchrist@vstretch ~/sandbox/perl
$ perl File-stat.pl
$st = bless( [
               20,
               970783,
               33188,
               1,
               13250,
               13250,
               0,
               0,
               1540094388,
               1540094388,
               1540094388,
               4096,
               0
             ], 'File::stat' );
1540094388


David