camel2snake-cli

Convert camelCase and PascalCase strings to snake_case from the command line. Zero dependencies.

$ camel2snake getElementById XMLParser parseHTTPResponse
get_element_by_id
xml_parser
parse_http_response

Why?

• API migrations — JavaScript → Python field mapping in one pipe
• Env var generation — camel2snake -u turns config keys into UPPER_SNAKE_CASE
• Acronym-aware — XMLParser → xml_parser, not x_m_l_parser
• Pipe-friendly — reads stdin, writes stdout, composes with any tool
• Zero dependencies — installs in ~1 second

Install

npm install -g @kszongic/camel2snake-cli

# Or use without installing
npx @kszongic/camel2snake-cli helloWorld

Usage

# Single string
camel2snake helloWorld
# hello_world

# Multiple strings
camel2snake getElementById XMLParser MyComponent
# get_element_by_id
# xml_parser
# my_component

# UPPER_SNAKE_CASE (perfect for env vars)
camel2snake -u databaseUrl apiKey jwtSecret
# DATABASE_URL
# API_KEY
# JWT_SECRET

# Pipe from stdin
echo "myVariable" | camel2snake
# my_variable

cat identifiers.txt | camel2snake

Options

Flag	Description
-u, --upper	Output UPPER_SNAKE_CASE
-h, --help	Show help
-v, --version	Show version

Conversion Examples

Input	Output	With -u
helloWorld	hello_world	HELLO_WORLD
getElementById	get_element_by_id	GET_ELEMENT_BY_ID
XMLParser	xml_parser	XML_PARSER
MyComponent	my_component	MY_COMPONENT
parseHTTPResponse	parse_http_response	PARSE_HTTP_RESPONSE
getURLForID	get_url_for_id	GET_URL_FOR_ID

Recipes

Generate .env.example from config keys

cat <<EOF | camel2snake -u
databaseUrl
redisHost
jwtSecret
maxRetryCount
EOF
# DATABASE_URL
# REDIS_HOST
# JWT_SECRET
# MAX_RETRY_COUNT

Map JS API fields to Python models

echo '{"firstName":"John","lastName":"Doe"}' \
  | node -e "process.stdout.write(Object.keys(JSON.parse(require('fs').readFileSync(0,'utf8'))).join('\n'))" \
  | camel2snake
# first_name
# last_name

Create a JS-Python field mapping

paste <(cat fields.txt) <(cat fields.txt | camel2snake) > mapping.tsv

Chain with other case converters

# camelCase → snake_case → kebab-case
echo "myVariableName" | camel2snake | snake2kebab
# my-variable-name

npm scripts

{
  "scripts": {
    "gen:env": "cat config-keys.txt | camel2snake -u > .env.example"
  }
}

Shell alias

alias c2s='camel2snake'
alias c2S='camel2snake -u'

How It Works

The converter scans each string character by character, inserting underscores at case boundaries. Consecutive uppercase characters (acronyms like XML, HTTP, URL) are treated as a single token rather than individual letters — so XMLParser correctly becomes xml_parser, not x_m_l_parser.

Use Cases

• Backend migrations — Convert field names between JS/TS and Python/Ruby/Rust conventions
• Environment variables — Generate UPPER_SNAKE_CASE env var names from config
• Database mapping — Map ORM fields to SQL column names
• Code generation — Automate naming in scaffolding tools
• CI/CD — Enforce naming conventions in pipelines

Comparison

Tool	Zero Deps	Cross-Platform	Stdin	Acronyms	UPPER_SNAKE
camel2snake-cli	✅	✅	✅	✅	✅
sed regex	✅	⚠️ GNU/BSD differ	✅	❌	Manual
change-case (lib)	❌	✅	❌	✅	✅
Python one-liner	❌ needs Python	✅	✅	❌	Manual
Online converters	N/A	Browser	❌	Varies	Varies

Related Tools

Part of the @kszongic case conversion family:

• snake2camel-cli — snake_case → camelCase
• kebab2camel-cli — kebab-case → camelCase
• kebab2snake-cli — kebab-case → snake_case
• snake2pascal-cli — snake_case → PascalCase
• pascal2snake-cli — PascalCase → snake_case

Other useful tools:

• env-lint-cli — Validate .env files
• dep-size — Check npm dependency sizes
• npm-name-check — Check npm name availability

License

MIT © 2026 kszongic