tee - Enhanced Output Redirection

The tee module executes a command and writes its output to both stdout and a specified file. Unlike traditional pipes, it preserves the original command's exit code and environment modifications.

When to Activate

• When logging build, test, or deployment outputs for CI/CD pipelines.
• When capturing both stdout and stderr while needing to react to command failures.
• When a command modifies environment variables that need to be maintained.

Core Principles & Rules

• Exit Code Integrity: Crucial for scripts where the following logic depends on the success of the logged command.
• Command Separation: Use the -- separator to distinguish between the output file and the command to run.
• Append Mode: Support for -a to append to the log file instead of overwriting.

Patterns & Examples

Log Build Output

# Capture build logs while ensuring the script stops on failure
x tee build.log -- make build

Capture Combined Output

# Log both stdout and stderr to a file
x tee /tmp/task.log -- eval 'npm run test 2>&1'

Logging Deployment

# Deploy and keep logs, allowing the exit code to be checked later
x tee deploy.log -- ./deploy.sh

Checklist

• Confirm if both stdout and stderr should be captured.
• Ensure the log file path is writable.
• Verify if append mode (-a) is required.