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29/Hostlist Format

This specification describes a compact form for expressing a list of hostnames which contain an optional numerical part.

Name github.com/flux-framework/rfc/spec_29.rst
Editor Mark A. Grondona <mgrondona@llnl.gov>
State raw

Language

Background

The hostlist is a somewhat well known format supported by existing HPC tools such as pdsh, powerman, and genders. The format is designed as a convenience on systems where hostnames are assigned with a common prefix, a numeric part, and an optional suffix. The result is a compact way to represent a possibly large list of hosts by name, e.g. prefix[0-1024].

This RFC details the Flux implementation of the hostlist format.

Implementation

A hostlist SHALL represent an ordered list of strings.

A hostlist string SHALL be a list of comma separated hostlist expressions.

A hostlist expression SHALL be a string of the form prefix[idlist]suffix, where all components prefix, [idlist], and suffix are OPTIONAL.

An empty hostlist expression, "", SHALL represent an empty list.

The prefix and suffix components of a hostlist expression SHALL consist of any printable, non-whitespace ASCII character besides the special characters including square brackets: "[ ]", and comma: ",".

An idlist SHALL represent an ordered list of non-negative integer ids.

An idlist MAY be a simple comma-separated list, e.g. 5,4,10,11,12,13.

Consecutive ids in an idlist MAY be compressed into hyphenated ranges, e.g. 5,4,11-13.

Leading zeros in the first element of an idlist SHALL be preserved across all ids in the list, e.g. 005,4,11-13 represents the list 005,004,011,012,013.

An idlist MAY contain repeated numbers, e.g. 2,2,2 is a valid list.

Within a hostlist expression, an idlist SHALL be enclosed in square brackets, e.g. host[0-10,12].

Test Vectors

  • "" = ""
  • "foox,fooy,fooz" = "foox,fooy,fooz"
  • "[1-3,5-6]" = "1,2,3,5,6"
  • "foo[1-5]" = "foo1,foo2,foo3,foo4,foo5"
  • "foo[0-4]-eth2" = "foo0-eth2,foo1-eth2,foo2-eth2,foo3-eth2,foo4-eth2"
  • "foo1,foo1,foo1" = "foo1,foo1,foo1"
  • "[00-02]" = "00,01,02"
  • "[00-2]" = "00,01,02"
  • "foo[1,1,2,1]" = "foo1,foo1,foo2,foo1"