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Claude with Skills

Exercise 02: Run a Skill Without the UI

Goal

Use claude -p to invoke the summarize-changes skill from the terminal without opening the interactive Claude Code interface.

Prerequisites

  • The summarize-changes skill installed at ~/.claude/skills/summarize-changes/SKILL.md (copy it from ../lesson-05-invoking/examples/summarize-changes/)
  • A git repository with at least one uncommitted change
  • claude available in your PATH

Step 1: Prepare a repository with changes

Find a git repository you are working in, or create a throwaway one:

Terminal window
mkdir /tmp/skill-test && cd /tmp/skill-test
git init
echo "hello" > hello.txt
git add hello.txt
git commit -m "initial"
echo "world" >> hello.txt

Now hello.txt has an unstaged change. The skill will summarize it.

Step 2: Run the skill headlessly

From inside the repository directory:

Terminal window
claude -p "/summarize-changes"

Claude Code starts, activates the skill, injects the diff output, produces a summary, and exits. You should see the summary printed to stdout.

Step 3: Capture the output to a file

Terminal window
claude -p "/summarize-changes" > summary.txt
cat summary.txt

The output is now in summary.txt. This is useful in CI pipelines where you want a diff summary saved as an artifact.

Step 4: Run the commit-message skill and use the output

Install the commit-message skill if you have not already:

Terminal window
cp -r path/to/lesson-03-repetitive-tasks/examples/commit-message ~/.claude/skills/

Stage a change and run:

Terminal window
git add hello.txt
COMMIT_MSG=$(claude -p "/commit-message")
echo "$COMMIT_MSG"

If the output looks correct, use it:

Terminal window
git commit -m "$COMMIT_MSG"

What claude -p does differently

claude -p exits after one turn. There is no back-and-forth. This means:

  • Skills that ask clarifying questions do not work well headlessly — Claude will ask a question and then the process exits before you can answer
  • Output is printed to stdout, so it can be piped or captured with standard shell tools
  • The exit code is 0 on success and non-zero on error, so you can use && and || in scripts
  • It is safe to use in CI/CD because the process always terminates

Stretch goal

Write a shell alias that stages all changes and generates a commit message in one command:

Terminal window
alias smart-commit='git add -A && git commit -m "$(claude -p "/commit-message")"'

Add this to your shell profile to make it permanent. Note: be careful with git add -A in real projects — review what is staged before committing.