$checkContains — Inline Substring Check

$checkContains tests whether a specified substring exists within a larger string. It is a compile-time-optimized function that returns the string "true" or "false". This is one of the most commonly used utility functions in BDFD for command detection, keyword filtering, and data validation.

How It Works

$checkContains[text;search] performs a case-sensitive substring search:

• $checkContains[Hello World;World] → "true"
• $checkContains[Hello World;world] → "false" (case mismatch)
• $checkContains[Hello World;xyz] → "false"
• $checkContains[Hello;] → "true" (empty string is contained in every string)

Compile-Time Optimization

When both text and search are literal constants, the check is evaluated at compile time and the result is baked in. This means keyword-based command routing can be extremely fast — the parser pre-computes which branch to take before the script ever runs.

When either argument contains a variable reference or function call, evaluation falls back to runtime.

Use in $if Conditions

$checkContains is most commonly used inside $if conditions to route commands based on user input:

$if[$checkContains[$message;ping]==true]
  Pong!
$endif

Always compare with ==true or ==false when using inside $if.

Case-Insensitive Searching

$checkContains is case-sensitive by design. To perform case-insensitive checks, convert both sides to lowercase:

$checkContains[$toLowercase[$message];$toLowercase[Admin]]

Common Use Cases

• Command detection: Check if a message contains a trigger word.
• Inventory checks: See if an item name appears in a list stored as a string.
• Filtering: Validate that user input contains expected content.
• Multi-keyword matching: Combine with $or to check for any of several keywords.

Common Pitfalls

• Case sensitivity: “Hello” does not contain “hello”. Use $toLowercase if case-insensitive matching is needed.
• Partial matches: $checkContains[sword;word] returns "true". Use exact equality checks or delimiters if you need whole-word matching.
• Empty search string: An empty needle always returns "true". Guard against empty user input if it matters.
• Type coercion: Both arguments are treated as strings. If you pass a number, it is converted to its string representation first.