hostlist_expression

Ruby gem for expanding hostlist expressions.

An expression like host-[1-3].com will expand into an array containing these elements:

host-1.com
host-2.com
host-3.com

This gem supports numeric and alphabetic ranges and sequences, and any combination.

By default both characters : (Ansible style) and - (pdsh style) are interpreted as range connectors.

Numeric ranges can have leading zeros [01-99]. If either bound has a leading zero, all numbers are padded to the width of the longest bound, so [1-010] expands to 001 through 010.

With commas you can define sequences: [1,3,5].

Ranges may be written in either direction, [9-1] expands the same as [1-9]. Duplicate hosts are removed from the result.

A complex example with all variations:

Expression: host-[A-C]-[c,d,001-003].com

Result:

host-A-c.com
host-A-d.com
host-A-001.com
host-A-002.com
host-A-003.com
host-B-c.com
host-B-d.com
host-B-001.com
host-B-002.com
host-B-003.com
host-C-c.com
host-C-d.com
host-C-001.com
host-C-002.com
host-C-003.com

Please note, in an alphabetic range both items are required to be either lowercase or uppercase, you can't mix. A range like [A-c] will raise a RuntimeError.

Requires Ruby 3.3 or newer.

gem install hostlist_expression

Or add it to your Gemfile:

gem "hostlist_expression"

require "hostlist_expression"
hosts = hostlist_expression("host-[1-3].com")
p hosts

# => ["host-1.com", "host-2.com", "host-3.com"]

The result is always an Array. Input without any range is returned as a single-element Array:

hostlist_expression("host.com")

# => ["host.com"]

You may optionally pass custom range connectors as the second argument, either a String or an Array of characters:

hosts = hostlist_expression("host-[1~3].com", "~")
hosts = hostlist_expression("host-[1~3,A-C,x/z].com", ["~", "-", "/"])

bundle install
bundle exec rake    # runs RuboCop and the RSpec suite

MIT