Path Component Common Ancestor

Find a lexical component-level common ancestor of normalized absolute POSIX paths; character-prefix and filesystem ancestry are not inferred.

Description

Find a lexical component-level common ancestor of normalized absolute POSIX paths; character-prefix and filesystem ancestry are not inferred.

A common path ancestor depends on whole components rather than a textual character prefix.

When to use this tool

Find a lexical component-level common ancestor of normalized absolute POSIX paths; character-prefix and filesystem ancestry are not inferred.

Prepare the supplied left, right fields for this operation.
Compare the complete example with the representation used by your own input before carrying the result into another step.

How to use the tool and how it works

Enter left, right. Use the exact text syntax, units and index conventions explained below.
Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
Read result.ancestor, result.sharedComponentCount. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.

Require absolute POSIX paths, collapse literal dot navigation and return slash plus their common leading component sequence, with sharedComponentCount.^[1]

Input field	Meaning and representation	Accepted input
left	left.	Text; at most 8,192 UTF-16 code units, subject to the grammar above
right	right.	Text; at most 8,192 UTF-16 code units, subject to the grammar above

Output field	Interpretation
result	Object containing the named outputs below.
result.ancestor	The ancestor value under the stated formula or text convention.
result.sharedComponentCount	The shared component count value under the stated formula or text convention.

json

{
  "input": {
    "left": "/a/b",
    "right": "/a/c"
  },
  "output": {
    "result": {
      "ancestor": "/a",
      "sharedComponentCount": 1
    }
  }
}

Limitations and assumptions

The root is returned when no components match. This is lexical ancestry, without symlink resolution or file existence checks.
Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
String lists have at most 128 entries of at most 128 code units; matrices have at most 128 rows and columns. Larger numeric lists and parsed JSON have separate bounded budgets. Nonfinite results and excessively large serialized outputs are rejected.
Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.

Alternative or Complementary methods

Use a filesystem-aware implementation with appropriate platform semantics for actual file operations. Literal slash components, Unicode comparison and filename plans do not resolve symlinks or atomically reserve a destination.

References

Tool behavior and example: Path Component Common Ancestor — tool.io

Similar or alternative tools

Path Component Relative Navigation
Plan lexical relative component navigation between absolute POSIX paths; no filesystem or symlink equivalence claim.
Path Component Name Budget Checker
Audit lexical POSIX component UTF-8 byte budgets against an explicit limit; not a universal NAME_MAX or filesystem encoding claim.