This secure coding standard consists of rules and recommendations.

Rules

Coding practices are defined to be rules when the following conditions are met:

1. Violation of the coding practice is likely to result in a security flaw that may result in an exploitable vulnerability.
2. Conformance to the coding practice can be determined through automated analysis, formal methods, or manual inspection techniques.

Implementation of the secure coding rules defined in this standard are necessary (but not sufficient) to ensure the security of software systems developed in the Perl programming language.

Rules are identified by the label rule.

Recommendations

Recommendations are guidelines or suggestions. Coding practices are defined to be recommendations when all of the following conditions are met:

1. Application of the coding practice is likely to improve system security.
2. One or more of the requirements necessary for a coding practice to be considered a rule cannot be met.

The set of recommendations that a particular development effort adopts depends on the security requirements of the final software product. Projects with high-security requirements can dedicate more resources to security and are consequently likely to adopt a larger set of recommendations.

To ensure that the source code conforms to this secure coding standard, it is necessary to have measures in place that check for rule violations. The most effective means of achieving this is to use one or more static analysis tools. Where a rule cannot be checked by a tool, then a manual review is required.

Recommendations are identified by the label recommendation.

Exceptions

Any rule or recommendation may specify a small set of exceptions detailing the circumstances under which the coding practice is not necessary to ensure the security of software. Exceptions are informative only and are not required to be followed.

Coding practices that specify one or more exceptions are identified by the label exceptions.

Identifiers

Each rule and recommendation is given a unique identifier. These identifiers consist of three parts:

• a three-letter mnemonic representing the section of the standard
• a two-digit numeric value in the range of 00–99
• the letters "PL" indicates that this is a Perl language guideline

The three-letter mnemonic can be used to group similar coding practices and to indicate to which category a coding practice belongs.

The numeric value is used to give each coding practice a unique identifier. Numeric values in the range of 00–29 are reserved for recommendations, while values in the range of 30–99 are reserved for rules.