shell-script

Shell Script Best Practices

Overview

Rules for writing robust, maintainable shell scripts in go-crypto-wallet. These rules are based on code review feedback and industry best practices.

Critical Shell Options

Always Use Strict Mode

set -euo pipefail

Explanation:

• -e: Exit immediately if any command fails
• -u: Treat unset variables as errors
• -o pipefail: Fail if any command in a pipeline fails (not just the last one)

Why pipefail matters:

# WITHOUT pipefail (BAD)
set -eu
cat nonexistent.txt | grep "pattern"  # Only grep's exit code matters

# WITH pipefail (GOOD)
set -euo pipefail
cat nonexistent.txt | grep "pattern"  # Fails immediately if cat fails

Variable Configuration

Make Hardcoded Values Configurable

Bad:

# Hardcoded volume name - brittle if project name changes
docker volume rm "go-crypto-wallet_wallet-mysql"

Good:

# Configurable with default
DOCKER_VOLUME_NAME="${DOCKER_VOLUME_NAME:-go-crypto-wallet_wallet-mysql}"
docker volume rm "$DOCKER_VOLUME_NAME"

Benefits:

• Flexibility for different environments
• No breakage if project structure changes
• Easy to override in CI/CD

Environment Variable Naming

Use descriptive, uppercase names with underscores:

RPC_USER="${RPC_USER:-xyz}"
RPC_PASSWORD="${RPC_PASSWORD:-xyz}"
WALLET_PASSPHRASE="${WALLET_PASSPHRASE:-test}"
DOCKER_VOLUME_NAME="${DOCKER_VOLUME_NAME:-go-crypto-wallet_wallet-mysql}"

Use Environment Variables Instead of Modifying Config Files

Bad (creates backups, modifies files):

# Backup and modify config file
sed -i.bak 's|host: "127.0.0.1:18332"|host: "127.0.0.1:18332/wallet/watch"|' config.yaml

# ... operations ...

# Restore backup
if [ -f "config.yaml.bak" ]; then
    mv "config.yaml.bak" "config.yaml"
fi

Good (use environment variables):

# Create wrapper function to set environment variable per-command
watch_with_wallet() {
    WALLET_BITCOIN_HOST="127.0.0.1:18332/wallet/watch" watch "$@"
}

# Use wrapper function
watch_with_wallet -c config.yaml create payment