Case converter for text and code

The tool splits your text into words first, then joins them in the style you pick. The same input, XML http request, in each case:

Text cases (Title, Sentence, UPPER, lower, Capitalized, alternating and inverse) keep your spaces and punctuation. Code cases turn each line into one name, so a pasted list of column names comes back as a list. A line that is a single code name, like get_user_by_email, is split into words first, so Title Case gives Get User by Email.

Most languages have a style guide that says which case goes where. The common ones:

Go is the odd one out: case is part of the language. Effective Go says a name is visible outside its package only when its first letter is upper case, and asks for MixedCaps instead of underscores. POSIX says the environment variables its utilities use are made of upper-case letters, digits and underscores, which is why DATABASE_URL looks the way it does.

To convert between code styles, the tool has to find the words inside a name first. It splits on:

• Anything that is not a letter or digit: spaces, _, -, ., /, emoji.
• A lower-case letter or digit followed by a capital: userId → user, Id; v2Api → v2, Api.
• The end of an acronym: XMLHttpRequest → XML, Http, Request; HTML5Parser → HTML5, Parser.

Apostrophes are dropped instead of splitting a word, so don't stop becomes dontStop, not donTStop. Letters with accents and non-Latin scripts are kept: größe der datei becomes GrößeDerDatei. To get plain ASCII for a URL, use the slug generator.

Style guides disagree on acronyms. PEP 8 says to capitalize all letters of an acronym in CapWords (HTTPServerError). The Google Java Style Guide treats them as normal words (XmlHttpRequest, newCustomerId). The "Keep acronyms" switch picks between the two.

Sentence case capitalizes only the first word of each sentence (and the word I). It is what most product UIs use for buttons and labels. Title case capitalizes the main words of a heading.

Here, title case keeps these words lower case unless they come first, last or right after a colon: a an the and but or nor for so yet as at by in of off on per to up via vs en if. Hyphenated words get each part handled (Step-by-Step), and words with their own capitals, like iPhone, JavaScript or NASA, are left alone. If a line is all caps, nothing can be told apart, so every word on it is treated the same.

AP, Chicago and APA style differ on details, for example whether longer prepositions like with or from are capitalized. Check your house style for anything you publish.

JavaScript: upper and lower case are built in. For identifier styles, Lodash has helpers.

'Hello World'.toUpperCase();   // 'HELLO WORLD'
'Hello World'.toLowerCase();   // 'hello world'

import { camelCase, snakeCase, kebabCase, startCase } from 'lodash';
camelCase('user profile id');  // 'userProfileId'
snakeCase('userProfileId');    // 'user_profile_id'
kebabCase('User Profile Id');  // 'user-profile-id'
startCase('user_profile_id');  // 'User Profile Id'

Python: str.title() treats an apostrophe as a word break, which the Python docs point out:

"they're bill's friends".title()   # "They'Re Bill'S Friends"
"Hello World".upper()               # 'HELLO WORLD'
"Hello World".lower()               # 'hello world'

import re
def snake(name):                    # 'userProfileId' -> 'user_profile_id'
    return re.sub(r'(?<=[a-z0-9])([A-Z])', r'_\1', name).lower()

Go: strings.Title is deprecated because it does not handle Unicode word breaks well. Use the golang.org/x/text/cases package.

import (
    "golang.org/x/text/cases"
    "golang.org/x/text/language"
)

cases.Title(language.English).String("hello world") // "Hello World"
strings.ToUpper("hello")                             // "HELLO"

Bash (version 4 or newer):

name="Hello World"
echo "${name^^}"   # HELLO WORLD
echo "${name,,}"   # hello world
echo "Hello" | tr '[:lower:]' '[:upper:]'   # HELLO, works in any POSIX shell

Other free tools that help with names and text: the slug generator for URLs, the JSON to TypeScript converter for typed field names, and the regex tester for custom renames. For editors and IDEs with rename refactoring built in, see IDE tools on DevHunt.