stream editor using javascript expressions

Usage no npm install needed!

<script type="module">
  import jpipe from '';


JPipe npm

stream editor using javascript


Run npm install -g jpipe, and then use the jp command as described:

  Usage: jp [options] <expression>

  A stream editor in javascript. Evaluates <expression> for each
  line of STDIN, where:

       _ = the current line
   _line = the current line number (starting at 0)
   _prev = the previous result of the expression
           (starts as '' or as [value] if --initial is set)

   chalk = the 'chalk' module.

   other modules are included with the -m flag. For example,
   '-m "module-name"' assigns 'require("module-name")' to


    -h, --help             output usage information
    -V, --version          output the version number
    -m, --module [module]  include a module in your expression
    -r, --reduce           print only the last value computed
    -i, --initial [value]  set the inital value of "_prev"
    -s, --swallow          swallow errors
    -t, --trim             trim whitespace from output
    -n, --nonewline        don't add newline (as `echo -n`)
    -f, --falsey           don't remove any falsy values


cat numbers.txt | jp '+_ + 10' > numbers_plus_ten.txt

Each line of the file numbers.txt is assigned to the variable _, and the result of +_ + 10 is printed to STDOUT, which is then redirected into numbers_plus_ten.txt.

If the result of this computation is a falsey value (other than 0, which is allowed for convenience), then it will not be output.


Some special values come bound in the expression you give jp:

  • _ is bound to the current line of the file.
  • _line is bound to the current line number of the file (starting at 0).
  • _prev is bound to the result of the last expression.
  • chalk is bound to the module chalk, which is very convenient for coloring output.

any additional modules you include with the -m flag will be required, and assigned to a camel-case variable name (module-name is assigned to moduleName). If you wish to include globally installed modules, make sure to add your global node_modules to NODE_PATH:

export NODE_PATH="$(npm prefix -g)/lib/node_modules:$NODE_PATH"


Print all lines of a file in yellow

cat text.txt | jp --falsey 'chalk.yellow(_)'

Sum all numbers in a file

cat numbers.txt | jp --reduce '+_prev + +_'

Sum second whitespace-separated column in a file

cat tabular.txt | jp --reduce '+_prev + +(_.split(/\s+/)[1])'`

Prepend every line with some random hex

cat text.txt | jp --module 'crypto' 'crypto.randomBytes(2).toString("hex") + " " + _'

Get field value from each line of a file (where each line is a JSON object)

cat objs.txt | jp 'JSON.parse(_).value'

Concatenate all arrays in a file of JSON arrays

cat rows.txt | jp --reduce --initial '[]' 'JSON.parse(_prev).concat(JSON.parse(_))'

List all .js files in green

ls | jp '_.match(/\.js$/)?'

Print all git commits whose hashes begin in a 7

git log --pretty=oneline | jp '_.charAt(0) === "7" && _'

Print some funky colored lines

yes | jp -n 'r = (Math.random() * 6) | 0;
  [,, chalk.yellow,, chalk.magenta, chalk.cyan][r]
  ((Math.random() * 2 | 0 % 2)? "____":"_/^\\_")'