pipeable-js (pjs)

pjs is a CLI tool that processes input from stdin or files using a streaming API. It applies operations in a specific order: filter, then map, then reduce.

To make one-liners easier, pjs automatically binds identifiers from String.prototype to the current line. You can also use specific variables to access data:

• $ : The current line (value).
• i : The current index.
• prev : The accumulated value (used in custom reduce expressions).
• curr : The current value (used in custom reduce expressions).
• array : The full array (used in custom reduce expressions).

Additionally, pjs provides access to:

• _ : Lodash functions.
• R : Ramda functions.
• $$ : Used for chaining expressions.

# Example of using $ and String.prototype methods
echo 'foo' | pjs -m 'toUpperCase()'

Install the pipeable-js package globally using npm to access the pjs command line tool.

npm install -g pipeable-js

Use the -m (or --map) flag to transform each line using a JavaScript expression. You can use $ to refer to the line or access String.prototype methods directly.

# Remove all digits
pjs -m "replace(/\d/g, '')" file

# Get second item of each line in a CSV
pjs -m 'split(",")[1]' file

pjs supports advanced functional programming patterns:

• Lodash: Access via the _ object.
• Ramda: Access via the R object.
• Chaining: Use $$ to chain expressions.

# Use Lodash to uppercase the first letter
echo 'hello' | pjs -m '_.upperFirst($)'

# Chain expressions using $$ and Lodash
echo 'please-titleize-this-sentence' | \
pjs -m '$$.lowerCase().split(" ").map(_.upperFirst).join(" ")'

# Use Ramda for point-free style
echo 'please-titleize-this-sentence' | \
pjs -m "R.compose(R.replace(/(^|\s)\w/g, R.toUpper), R.replace(/-/g, ' '))"

Use the -j (or --json) flag to output results as a JSON array. This is useful when combining the current line ($) with other properties in a map operation.

(echo 'foo' && echo 'foobar') | pjs -jm '{name: $, length: length}'
# Output:
# [
#   {"name":"foo","length":3},
#   {"name":"foobar","length":6}
# ]

Use the -f (or --filter) flag to keep only lines that satisfy a boolean expression. Expressions can use length (from String.prototype) or i (the index).

# Print all odd lines (using index i)
pjs -f 'i % 2 == 0' file

# Print all lines greater than 80 chars in length
pjs -f 'length > 80' file

Use the -r (or --reduce) flag to aggregate lines into a single value. You can use built-in function names or custom expressions using prev and curr.

Built-in functions: length, min, max, sum, avg, concat.

# Count lines in a file using built-in length
pjs -r length file

# Sum all decimal numbers in a file using a custom expression
pjs -r 'Number(prev) + Number(curr)' file

# Concatenate all lines in multiple files
pjs -r concat file1 file2

The pjs command accepts options and optional file arguments. Operations are executed in the order: filter $\rightarrow$ map $\rightarrow$ reduce.

Options:

• -h, --help: Output usage information.
• -V, --version: Output the version number.
• -i, --ignore: Ignore empty lines.
• -j, --json: Output results as JSON.
• -f, --filter <exp>: Filter lines by a boolean expression.
• -m, --map <exp>: Map values using the expression.
• -r, --reduce <func|exp>: Reduce using a built-in function or a custom expression.

Built-in reduce functions: length, min, max, sum, avg, concat.

Usage: pjs [options] [files ...]

The following flags are available for the pjs command line interface:

Exit Codes

• 3: Invalid expression syntax (SyntaxError or ReferenceError).
• 1: Other uncaught exceptions.

pjs --help