I am observing subtle differences between tempfiles created by the two interfaces of File::Temp -- the functional and the object-oriented. These differences do not show up when you 'diff' or 'vimdiff' two files. They only show up when you take a digest of the two files (e.g., via Digest::MD5->hexdigest) or compare the two files with File::Compare.

First, File::Temp's functional interface. Suppose I write the same content to two different tempfiles, then compare the resulting tempfiles in two ways: (1) a wrapper around Digest::MD5->hexdigest; and (2) File::Compare::compare().

#!perl
use 5.14.0;
use warnings;
use Carp;
use Data::Dumper;
use Digest::MD5;
use File::Compare (qw| compare |);
use File::Temp qw( tempfile );
use Test::More;

my $basic       = 'x' x 10**2;
my @digests;

my ($fh1, $t1) = tempfile();
for (1..100) { say $fh1 $basic }
close $fh1 or croak "Unable to close $t1 after writing";
push @digests, hexdigest_one_file($t1);

my ($fh2, $t2) = tempfile();
for (1..100) { say $fh2 $basic }
close $fh2 or croak "Unable to close $t2 after writing";
push @digests, hexdigest_one_file($t2);

say Dumper [ @digests ];

cmp_ok($digests[0], 'eq', $digests[1],
    "Same md5_hex for $t1 and $t2");

is(compare($t1, $t2), 0, "compare() indicates no differences between $
+t1 and $t2");

done_testing();

sub hexdigest_one_file {
    my $filename = shift;
    say "Filename: $filename";
    my $state = Digest::MD5->new();
    open my $FH, '<', $filename or croak "Unable to open $filename for
+ reading";
    $state->addfile($FH);
    close $FH or croak "Unable to close $filename after reading";
    return $state->hexdigest;
}
[download]

Let's run the file:

$ prove -v hexdig1.t 
hexdig1.t .. 
Filename: /tmp/0qZ8en3x1Y
Filename: /tmp/GQuMULnyLM
$VAR1 = [
          'e395fd01f84d7d1006a99e2a6b8fb832',
          'e395fd01f84d7d1006a99e2a6b8fb832'
        ];
ok 1 - Same md5_hex for /tmp/0qZ8en3x1Y and /tmp/GQuMULnyLM
ok 2 - compare() indicates no differences between /tmp/0qZ8en3x1Y and 
+/tmp/GQuMULnyLM
1..2
ok
All tests successful.
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Second, let's use File::Temp's object-oriented interface. We'll create two objects and write the same content with each, then compare the files generated in the same ways as above.

#!perl
use 5.14.0;
use warnings;
use Carp;
use Data::Dumper;
use Digest::MD5;
use File::Compare (qw| compare |);
use File::Temp qw( tempfile );
use Test::More;

my $basic       = 'x' x 10**2;
my @digests;

my $t3 = File::Temp->new( UNLINK => 0);
for (1..100) { say $t3 $basic }
push @digests, hexdigest_one_file($t3);

my $t4 = File::Temp->new( UNLINK => 0);
for (1..100) { say $t4 $basic }
push @digests, hexdigest_one_file($t4);

say Dumper [ @digests ];

cmp_ok($digests[0], 'eq', $digests[1],
    "Same md5_hex for $t3 and $t4");

is(compare($t3, $t4), 0, "compare() indicates no differences between $
+t3 and $t4");

done_testing();

sub hexdigest_one_file {
    my $filename = shift;
    say "Filename: $filename";
    my $state = Digest::MD5->new();
    open my $FH, '<', $filename or croak "Unable to open $filename for
+ reading";
    $state->addfile($FH);
    close $FH or croak "Unable to close $filename after reading";
    return $state->hexdigest;
}
[download]

Let's run the file:

$ prove -v hexdig2.t 
hexdig2.t .. 
Filename: /tmp/vO_5WGnJ2V
Filename: /tmp/3nw1qtQRAm
$VAR1 = [
          '24676db37df646bab175feedec39259d',
          '24676db37df646bab175feedec39259d'
        ];
ok 1 - Same md5_hex for /tmp/vO_5WGnJ2V and /tmp/3nw1qtQRAm
ok 2 - compare() indicates no differences between /tmp/vO_5WGnJ2V and 
+/tmp/3nw1qtQRAm
1..2
ok
All tests successful.
[download]

But third, let's use both File::Temp interfaces within the same file. Once again, we'll write the same content and use two ways of comparing the output.

#!perl
use 5.14.0;
use warnings;
use Carp;
use Data::Dumper;
use Digest::MD5;
use File::Compare (qw| compare |);
use File::Temp qw( tempfile );
use Test::More;

my $basic       = 'x' x 10**2;
my @digests;

my ($fh1, $t1) = tempfile();
for (1..100) { say $fh1 $basic }
close $fh1 or croak "Unable to close $t1 after writing";
push @digests, hexdigest_one_file($t1);

my $t3 = File::Temp->new( UNLINK => 0);
for (1..100) { say $t3 $basic }
push @digests, hexdigest_one_file($t3);

say Dumper [ @digests ];

cmp_ok($digests[0], 'eq', $digests[1],
    "Same md5_hex for $t1 and $t3");

is(compare($t1, $t3), 0, "compare() indicates no differences between $
+t1 and $t3");

done_testing();

sub hexdigest_one_file {
    my $filename = shift;
    say "Filename: $filename";
    my $state = Digest::MD5->new();
    open my $FH, '<', $filename or croak "Unable to open $filename for
+ reading";
    $state->addfile($FH);
    close $FH or croak "Unable to close $filename after reading";
    return $state->hexdigest;
}
[download]

Let's run the file:

$ prove -v hexdig3.t 
hexdig3.t .. 
Filename: /tmp/zgeqEkMDL8
Filename: /tmp/TrjkWZFjs2
$VAR1 = [
          'e395fd01f84d7d1006a99e2a6b8fb832',
          '24676db37df646bab175feedec39259d'
        ];
not ok 1 - Same md5_hex for /tmp/zgeqEkMDL8 and /tmp/TrjkWZFjs2

#   Failed test 'Same md5_hex for /tmp/zgeqEkMDL8 and /tmp/TrjkWZFjs2'
#   at hexdig3.t line 25.
#          got: 'e395fd01f84d7d1006a99e2a6b8fb832'
#     expected: '24676db37df646bab175feedec39259d'
not ok 2 - compare() indicates no differences between /tmp/zgeqEkMDL8 
+and /tmp/TrjkWZFjs2

#   Failed test 'compare() indicates no differences between /tmp/zgeqE
+kMDL8 and /tmp/TrjkWZFjs2'
#   at hexdig3.t line 28.
#          got: '1'
#     expected: '0'
1..2
# Looks like you failed 2 tests of 2.
Dubious, test returned 2 (wstat 512, 0x200)
Failed 2/2 subtests 

Test Summary Report
-------------------
hexdig3.t (Wstat: 512 Tests: 2 Failed: 2)
  Failed tests:  1-2
  Non-zero exit status: 2
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Both my wrapper around Digest::MD5->hexdigest() and File::Compare::compare() indicate that the files created by the two different File::Temp interfaces differ from each other. But if I examine those files with, say, 'diff' or 'od -c', I don't get any differences!

[tmp] $ ls -l /tmp/zgeqEkMDL8 /tmp/TrjkWZFjs2
-rw------- 1 jkeenan jkeenan 10100 Aug 29 12:46 /tmp/TrjkWZFjs2
-rw------- 1 jkeenan jkeenan 10100 Aug 29 12:46 /tmp/zgeqEkMDL8
[tmp] $ diff /tmp/zgeqEkMDL8 /tmp/TrjkWZFjs2
[tmp] $
[download]

Can anyone explain these anomalies? Thank you very much.