JavaScript: Functional Programming for JavaScript Developers

Filters and pipes

If you're at all familiar with the Unix command line or, to a lesser extent, the Windows command line, then you'll have probably made use of pipes. A pipe, which is represented by the | character is shorthand for "take the output of program A and put it into program B". This relatively simple idea makes the Unix command line incredibly powerful. For instance, if you wanted to list all the files in a directory and then sort them and filter for any which start with either the letters b or g and end with an f then the command might look like the following:

ls|sort|grep "^[gb].*f$"

The ls command lists all files and directories, the sort command sorts them, and the grep command matches file names against a regular expression. Running ...