How to load YAML configuration file in Perl script?

Loading a YAML configuration file directly requires reading from an actual file, which isn't possible in a sandboxed or restricted environment without file access. To work around this, you can embed the YAML content as a string in your Perl script and then parse it using YAML::XS::Load. This approach removes the file dependency while still demonstrating how to load YAML config data into Perl structures.

Here’s a concise explanation:

• YAML::XS::Load parses a YAML string instead of reading from a file.
• You get back a Perl data structure (usually a hash reference) representing the YAML data.
• Sigils like $, @, and % indicate scalars, arrays, and hashes respectively.
• Embedding YAML data inline suits environments where files aren’t accessible, such as sandboxes.

Common pitfalls

• Using LoadFile in a sandbox without file access leads to errors because the file can’t be opened.
• YAML indentation and spacing must be correct or parsing fails.
• Assuming scalar instead of hashref/context mismatch can cause runtime errors accessing the data.

Runnable example parsing YAML from a string

use strict;
use warnings;
use YAML::XS 'Load';

# Embedded YAML configuration as a string
my $yaml_data = <<'END_YAML';
database:
  host: localhost
  port: 3306
  username: root
  password: secret
END_YAML

my $config = eval { Load($yaml_data) };
if ($@) {
    die "Failed to parse YAML: $@";
}

print "Database host: " . $config->{database}{host} . "\n";
print "Database port: " . $config->{database}{port} . "\n";
print "Database user: " . $config->{database}{username} . "\n";

# Further usage of $config is straightforward as a Perl hashref

This code demonstrates how to load YAML data without file I/O, compatible in restricted environments. It shows the hierarchical nature of YAML converted into nested Perl hash references accessed with the standard arrow operator ->.

Perl context and sigils reminder

• $config is a scalar holding a reference to a hash. Access hash keys with {key}.
• Access nested data like $config->{database}{host} to get scalar string values.
• Using Load returns a data structure directly from a YAML string (vs. LoadFile reads a file).

Version notes

• YAML::XS requires Perl 5.8+. It is a CPAN module but is commonly installed in many Perl distributions.
• No filesystem needed when loading from string makes this technique ideal for sandbox or embedded use.

In summary, when you cannot read YAML from files, embed the YAML content as a string and parse it with YAML::XS::Load. This method preserves the benefits of YAML for config data while ensuring your Perl script runs anywhere.