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

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

• 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

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

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"

Remove comments:

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

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

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.

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