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get-session-id

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Reference for accessing session ID via ${CLAUDE_SESSION_ID} automatic substitution

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Source SKILL.md: https://github.com/cowwoc/cat/blob/HEAD/plugin/skills/get-session-id/SKILL.md

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Get Session ID Skill

Purpose: The session ID is automatically available in skills and commands via ${CLAUDE_SESSION_ID}.

How It Works:

  • Claude Code substitutes ${CLAUDE_SESSION_ID} with the actual session ID when loading skills
  • No manual extraction or lookup required
  • The session ID is also visible in context via SessionStart hooks for user reference

When to Use This Skill:

  • Reference this documentation to understand how session IDs work
  • The session ID is already available - just use ${CLAUDE_SESSION_ID} in skill/command templates

How Session IDs Work

Claude Code assigns a unique session ID (UUID v4) to each conversation session. This ID is used for:

  • Naming conversation history files: /home/node/.config/projects/-workspace/{session-id}.jsonl
  • Session-specific TODO list tracking
  • Hook coordination across tools
  • Task ownership in multi-instance scenarios

Automatic Substitution in Skills

In skill and command markdown files, use ${CLAUDE_SESSION_ID} directly:

# This gets auto-substituted when the skill loads
SESSION_FILE="/home/node/.config/claude/projects/-workspace/${CLAUDE_SESSION_ID}.jsonl"
cat "$SESSION_FILE" | jq -s 'length'

Hooks and Scripts

Bash hooks receive the session ID via stdin JSON:

# Read stdin JSON and extract session_id
INPUT=$(cat)
SESSION_ID=$(echo "$INPUT" | jq -r '.session_id // empty')

# Use for session-specific operations
SESSION_FILE="/home/node/.config/claude/projects/-workspace/${SESSION_ID}.jsonl"

User Visibility

The session ID is injected into conversation context via two mechanisms:

  • echo-session-id.sh: Outputs session ID at SessionStart
  • inject-session-instructions.sh: Includes session ID in CAT instructions

Users see the session ID in system reminders at conversation start:

Session ID: b6933609-ab67-467e-af26-e48c3c8c129e

Usage Examples

Example 1: In Skill Templates

# Session ID is auto-substituted - no manual lookup needed
cat /home/node/.config/projects/-workspace/${CLAUDE_SESSION_ID}.jsonl | jq -s 'length'

Example 2: Access Session History

# The session ID is already substituted when this runs
jq -s '[.[] | select(.type == "message")]' \
  "/home/node/.config/projects/-workspace/${CLAUDE_SESSION_ID}.jsonl"

Example 3: In Hook Scripts (stdin JSON)

#!/bin/bash
INPUT=$(cat)
SESSION_ID=$(echo "$INPUT" | jq -r '.session_id // empty')
# Now use $SESSION_ID for session-specific operations

Related

  • echo-session-id.sh: Hook that outputs session ID for user visibility
  • inject-session-instructions.sh: Hook that includes session ID in CAT instructions
  • get-history: Skill that uses session ID to access conversation