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Claude with Skills

Lesson 06: Paths and Shell

Two fields control where and how a skill activates: paths restricts auto-activation to specific file contexts, and shell sets the interpreter used for dynamic context injection commands.

The paths field

What it does

When paths is set, the skill only auto-activates when the user is working with files that match one of the glob patterns. “Working with” means the file is open, being edited, or referenced in the current task.

paths:
  - "src/components/**"
  - "src/pages/**"

A skill with this configuration will not auto-activate when the user is editing a migration file or a backend route. It only surfaces when the context involves component or page files.

What it does NOT do

paths does not prevent you from invoking the skill directly. If you type /frontend-only-lint while editing a backend file, the skill runs. Path restrictions only affect auto-invocation — when Claude decides on its own to activate a skill based on its description.

Why use it

Without path restrictions, a skill’s description keywords might match contexts where the skill is not useful. A “check React component props” skill that activates during a Python debugging session is noise. paths makes auto-invocation precise.

Glob pattern syntax

Patterns follow standard glob conventions:

  • * — matches any characters within a single path segment
  • ** — matches any number of path segments (including zero)
  • ? — matches exactly one character
  • {a,b} — matches either a or b

Examples:

  • "src/components/**" — any file anywhere under src/components/
  • "**/*.sql" — any .sql file in any directory
  • "migrations/**" — any file under a migrations/ directory at any depth
  • "**/*.{test,spec}.{ts,js}" — any test file in TypeScript or JavaScript
  • "db/migrate/**" — files under db/migrate/ specifically

Combining multiple patterns

List multiple patterns to cover related locations:

paths:
  - "src/components/**"
  - "src/pages/**"
  - "src/hooks/**"

The skill auto-activates if the current file matches any of the listed patterns.

The shell field

What it does

shell sets the interpreter used to run dynamic context injection commands (the !`cmd` and ```! blocks in the skill body).

shell: bash
shell: powershell

Default

bash is the default. On macOS and Linux, leave this field unset.

When to set shell: powershell

On Windows, if your dynamic context injection commands use PowerShell syntax (for example, $env:PATH, Get-ChildItem, or Select-Object), set shell: powershell.

PowerShell injection also requires the environment variable CLAUDE_CODE_USE_POWERSHELL_TOOL=1 to be set. Without it, the field is accepted but may not take effect.

Portability note

Skills that use shell: powershell do not run correctly on macOS or Linux. If you want a cross-platform skill, write injection commands in POSIX shell syntax and leave shell unset.

Examples

  • examples/frontend-only-lint/ — uses paths to restrict auto-activation to frontend component files

Next lesson

Lesson 07: Model and effort