Question

I would like to use file locking on yaml files, but how do I get a file handle for the yaml file?

#!/usr/bin/perl

use strict;
use YAML::Syck;
use Fcntl ':flock';

use warnings;

my $cfg = YAML::Syck::LoadFile('t.yaml');

# need a handle

flock($fh, LOCK_EX) or die "couldn't get lock: $!\n";

$cfg->{a} = 1;

close $fh;

Update

Based on the answers I have now tried the following, but it always writes an empty invalid yaml file.

#!/usr/bin/perl
use strict;
use YAML::Syck;
use Fcntl ':flock';
use warnings;

open my $fh, ">t.yaml";

my $cfg = YAML::Syck::LoadFile($fh);

flock($fh, LOCK_EX) or die "couldn't get lock: $!\n";

$cfg->{a} = 1;

my $yaml = YAML::Syck::Dump($cfg);
$yaml::Syck::ImplicitUnicode = 1;

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

Answer 1

Note that according to its documentation LoadFile also accepts filehandle. You can open first, flock and pass handle to LoadFile.

Edit: I would use something like this:

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

open my $fh, '+<', 't.yaml';
flock($fh, LOCK_EX) or die "couldn't get lock: $!\n";

my $cfg = YAML::Syck::LoadFile($fh);

$cfg->{a} = 1;
$cfg->{b} = 2;

my $yaml = YAML::Syck::Dump($cfg);
$YAML::Syck::ImplicitUnicode = 1;

seek $fh,0, SEEK_SET;   # seek back to the beginning of file
print $fh $yaml;
close $fh;