Question

When I run the below script I get a corrupt yaml file like so

--- 
1: 
  name1: abc
  name2: abc
---
me3: abc
---

Question

Can anyone see that I am doing wrong?

#!/usr/bin/perl

use strict;
use YAML::Syck;
use Fcntl ':flock', 'SEEK_SET';
use warnings;
use Data::Dumper;

my $acc;
my $acc_fh;

$acc->{1}{name1} = "abc";

unlink 'test.yaml';

# write initial
open F, '>', 'test.yaml';
print F YAML::Syck::Dump($acc);
close F;


($acc, $acc_fh) = read_yaml_with_lock('test.yaml');
$acc->{1}{name2} = "abc";
$acc->{1}{name3} = "abc";
write_yaml_with_lock($acc, $acc_fh);

($acc, $acc_fh) = read_yaml_with_lock('test.yaml');
delete $acc->{1}{name3};
write_yaml_with_lock($acc, $acc_fh);


sub read_yaml_with_lock {
    my ($file) = @_;

    open my $fh, '+<', $file or die $!;
    flock($fh, LOCK_EX) or die $!;

    my $obj = YAML::Syck::LoadFile($fh); # this dies on failure
    return ($obj, $fh);
}

sub write_yaml_with_lock {
    my ($obj, $fh) = @_;

    my $yaml = YAML::Syck::Dump($obj);
    $YAML::Syck::ImplicitUnicode = 1;
    seek $fh, 0, SEEK_SET;   # seek back to the beginning of file

    print $fh $yaml . "---\n";
    close $fh;
}

Answer 1

You write to the same file twice. During the second time the YAML code you’re writing is shorter than the first time because you delete that hash key inbetween the calls. However, you neither unlink the file after the first time nor do you truncate it after writing to it the second time. So what you see as corruption is the part of the file that has been written the first time but that hasn’t been overwritten the second time.