essed

essed is a simple program with purpose similar to sed or awk

Pros and cons

When to use essed

• Dealing with line-delimited JSON
• One-time time-consuming task
• Playing around
• Want to leverage knowledge of JavaScript

When not to use essed

• Performance - sed is strongly optimized C code. JavaScript is much slower. It's totally possible for essed to be 200 times slower than C-based tools.
• Non-UTF8 encodings (at least yet)
• Dealing with binary files

Consider

• Portability - you can use essed in your npm scripts. Though, it won't be installed globally on your CI.

TODO

• Loading code from file
• assert - assert input match some criteria. If it doesn't, break pipeline, otherwise return untouched
• find - find first line matching some criteria
• limit parameter on filter - if number of matched items exceed limit, drop them down
• limit parameter on map
• takeWhile
• takeUntil
• findLast
• reduce
• Native support for line-delimited JSON
• Provide Webpack compiled build to improve startup time
• Provide way to load external modules

map

Examples

Remove whitespace from each line:

cat ~/.bashrc | essed --map "line.trim()"

Reverse lines:

cat ~/.bashrc | essed --map "$0.reverse()"

Remove comments (nulls and undefineds are filtered out from output):

cat ~/.zshrc | essed --map "value.trim().startsWith('#') ? null : line"

Color even lines (terminal):

cat ~/.zshrc | essed -m "i % 2 ? line.yellow : line"

filter

Examples

Remove comments:

essed --filter "line.trim().startsWith('#')" ~/.zshrc

Comming

Allowed return values

• string
• Promise<string>
• highland<string>
• ReadableStream<string>

Enviroment

For your convenience we expose following "globals":

• shared - empty object shared by many invocations
• P, Bluebird - Bluebird instance
• lodash, _ - lodash instance
• hl, highland - highland instance
• deburr, pad, trim, truncate, upperFirst, replace - exported from lodash
• execFile, execFileSync - exported from native child_process
• colors - colors instance
• log - function that logs it's input on stderr and returns first argument.
• fs - native Node.js module ** log(line) === line

colors module is avalaible by default.

Line is available as line, l, value, $0.

Number of line is avalaiable as i and index.

Resources to read:

• Libraries used
  • child_process
  • lodash
  • highland
  • bluebird
  • colors
• Recipes
• jq - can be better choice for JSON-heavy jobs