node package manager


Node CLI Filter -- Do one liners easier


If you've used perl oneliners before you're expecting when you pass -pe to node that you'll evaluate the script once per input line

$ echo -e "foo\nbar" | perl -pe '"baz"'

However if you try it:

$ echo -e "foo\nbar" | node -pe '"baz"'

nf is a small package that lets you perform arbitrary javascript/node actions once per input line:

$ npm install -g nf
$ echo -e "foo\nbar" | nf -pe '"baz"'

Valid command line arguments:

  • -e -- evaluate the given script (if not passed assumes last argument is a javascript file to load)
  • -n -- evaluate the given script once per input line, the current line is available in the global __line
  • -p -- evaluate the given script once per input line with an implicit print of the return value (implies -n)

Here's a small example interpreting the current line

$ echo -e "foo\nbaz\nfoobar" | nf -pe '__line.replace(/foo/, "bar")'

Here is apache.js which transforms an apache log line to json:

var pattern = /^(\S+)\s+(\S+)\s+(\S+)\s+\[(.+)\]\s+(.+)\s+(.+)\s+(HTTP\/\d+.\d+)\s+"(\d+)"\s+(\S+)\s+"(.*)"\s+"(.*)"\s+"(.*)"$/;
(function(line) {
  var m = line.match(pattern);
  if (!m) return JSON.stringify({});
  var obj = {
    host: m[1],
    a: m[2],
    user: m[3],
    date: m[4],
    method: m[5],
    url: m[6],
    version: m[7],
    statusCode: m[8],
    contentLength: m[9],
    refer: m[10],
    userAgent: m[11],
  return JSON.stringify(obj);

then using jsontool you can find the uniq userAgents

cat access.log | nf -p ./apache.js | json -ga userAgent | sort -r | uniq | head 10
Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:21.0) Gecko/20100101 Firefox/21.0
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0
Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.110 Safari/537.36
Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.64 Safari/537.31
Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.64 Safari/537.31
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/536.30.1 (KHTML, like Gecko) Version/6.0.5 Safari/536.30.1
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.37 Safari/537.36
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.110 Safari/537.36
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.110 Safari/537.36
Mozilla/4.0 (compatible;)

Scripts (either in string form or from a file) are not the same thing as a node module; most but not all the globals you expect are there. You can require in your script, but notably exports and module are missing as their utility would be suspect.