Cross-platform pipe command in NPM script

Question

Considering we have NPM script with a pipe, similarly to what's suggested in Istanbul documentation:

"coveralls": "cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls"

It obviously doesn't take Windows into account.

How can such command with a pipe be made cross-platform in Node.js package?

The question is specific to Coveralls but isn't limited to it; this could be any command with a pipe.

Answer 1

Both Bash and the Windows command line (e.g. cmd.exe and PowerShell) have the pipe operator (|) so that shouldn't be a concern regarding cross-platform compatibility.

Given your example npm-script, the primary incompatibility regarding cross-platform support is usage of Bash's cat command. Usage of cat will fail via Windows cmd.exe, however cat is supported via Windows PowerShell.

To circumvent the aforementioned cross-platform issue regarding cat, consider utilizing a nodejs utility script as follows. Let's name the file cat.js:

cat.js

const fs = require('fs');

fs.readFile(process.argv[2], function(err, data) {
  process.stdout.write(data);
});

As you can see, it utilizes nodes builtin:

• fs.readFile to read the contents of a file.
• The file path of the file to read will be provided as an argument to the script and captured using process.argv.
• The contents of the file is the written to process.stdout

_{Note: For the sake of brevity cat.js doesn't include any error capturing/handling, so you may wish to add some.}

npm script

Then in your scripts section of your package.json we invoke cat.js and pass the path to the file (i.e. ./coverage/lcov.info) as an argument. For instance:

"scripts": {
  "coveralls": "node cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls"
},

_{Note: The npm-script above assumes cat.js resides in the same directory and level as package.json. If you choose to locate it elsewhere the path to it will need to be redefined. E.g. "node path/to/cat ./coverage/lcov.info | ..."}

So long as the nodejs file specified on the right hand of the pipe (|) utilizes process.stdin to read from stdin, i.e file descriptor 0, (as coveralls.js does) using the pipe cross-platform will be OK.

Answer 2

While I have not used Windows in some time, its CMD.EXE command line processor supports command redirection as well as “piping” the output of one program to the input of another.

See Syntax Redirection for more information.

For piping programmatically, see the pipe-operator NPM module for a Node/JavaScript implementation of shell piping.