Shell Error Debug Workflow

Shell Error Debug Workflow

When run_shell returns an 'unknown error' or ambiguous failure, apply this systematic troubleshooting workflow to diagnose and resolve the issue.

When to Use This Skill

• run_shell returns an 'unknown error' message
• Shell command fails without clear error output
• Command works locally but fails in the agent environment
• Intermittent or unexplained shell failures

Step-by-Step Troubleshooting Workflow

Step 1: Capture Explicit Stderr

Redirect stderr to stdout to capture all error output:

# Instead of:
run_shell command="some-command"

# Use:
run_shell command="some-command 2>&1"

This ensures error messages are captured in the output rather than being lost.

Step 2: Verify Working Directory

Confirm the current working directory and its contents:

run_shell command="pwd && ls -la"

Check that:

• You're in the expected directory
• Required files/directories exist
• Permissions are correct

Step 3: Check Tool/Command Availability

Verify the required command or tool exists and is accessible:

run_shell command="which some-command || command -v some-command || type some-command"

If the tool is not found, check PATH or install the required package.

Step 4: Use Absolute Paths

Replace relative paths with absolute paths to avoid directory-related issues:

# Instead of:
run_shell command="python script.py"

# Use:
run_shell command="$(pwd)/script.py"
# or
run_shell command="/absolute/path/to/script.py"

Step 5: Test with Minimal Command

Isolate the issue by running a minimal version of the command:

# Test basic functionality first
run_shell command="echo 'test'"

# Then gradually add complexity
run_shell command="some-command --version"
run_shell command="some-command --help"

Step 6: Check Environment Variables

Some commands depend on specific environment variables:

run_shell command="env | grep -i relevant_var"

Complete Diagnostic Sequence

For persistent unknown errors, run this complete diagnostic:

# 1. Capture full environment
run_shell command="pwd && echo '---' && ls -la && echo '---' && env"

# 2. Test command with full error capture
run_shell command="your-command 2>&1 | head -50"

# 3. Check command availability
run_shell command="which your-command || echo 'Command not found in PATH'"

# 4. Try with absolute path
run_shell command="/full/path/to/your-command 2>&1"

Common Causes and Solutions

Example: Troubleshooting a Python Script Failure

# Initial failing command
run_shell command="python process.py"
# Returns: unknown error

# Apply diagnostic workflow:
# Step 1: Capture stderr
run_shell command="python process.py 2>&1"

# Step 2: Verify directory
run_shell command="pwd && ls -la"

# Step 3: Check Python availability
run_shell command="which python && python --version"

# Step 4: Use absolute path
run_shell command="$(pwd)/process.py 2>&1"
# or
run_shell command="/usr/bin/python3 $(pwd)/process.py 2>&1"

Best Practices

1. Always capture stderr when debugging: 2>&1
2. Verify assumptions about working directory and file locations
3. Start simple before running complex commands
4. Use absolute paths in production/repeatable scripts
5. Check tool versions when behavior seems inconsistent
6. Document environment when errors are hard to reproduce

When to Escalate

If this workflow does not resolve the issue:

• The error may be environmental (container/runtime specific)
• Consider using shell_agent for complex shell tasks that require autonomous error handling
• Check for resource constraints (disk space, memory, timeouts)