Comparing Kubernetes versions in shell script

README.md

The attached script provides a function for comparing Kubernetes versions in shell script. It's possible for the script to validate itself by invoking it with TEST_SEMVER_COMP=1:

$ TEST_SEMVER_COMP=1 semver.sh 
              a               b   exp   act
           v1.0            v1.0     0     0
          v10.0            v1.0     1     1
           v1.0           v10.0   255   255
          v1.14    v1.14.alpha1     1     1
   v1.14.alpha1           v1.14   255   255
  v1.140.alpha1           v1.14     1     1

semver.sh

#!/bin/sh

set -e
set -o pipefail

# Extracts the MAJOR.MINOR.PATCH.BUILD portion of a semantic version string.
mmpb() {
  echo "${1}" | sed -e 's/^\(v\{0,1\}\)\([[:digit:]]\{1,\}.[[:digit:]]\{1,\}\)\(.[[:digit:]]\{1,\}\)\{0,1\}\(.[[:digit:]]\{1,\}\)\{0,1\}\(.\{0,\}\)$/\1\2\3\4/g'
}

# Returns 0 if $1>$2
version_gt() {
  test "$(printf '%s\n' "${@}" | sort -V | head -n 1)" != "${1}"
}

# Compares two semantic version strings:
#   0 if eq
#   1 if a>b
# 255 if a<b
semver_comp() {
  va="${1}"; vb="${2}"

  # If the strings are exactly the same then return 0 to indicate the versions
  # are equal.
  [ "${va}" = "${vb}" ] && return 0

  # Get the MAJOR.MINOR.PATCH.BUILD string for each version.
  vaMMPB="$(mmpb "${va}")"; vbMMPB="$(mmpb "${vb}")"

  # If the original versions are the same as the strings that are just
  # MAJOR.MINOR.PATCH.BUILD, then it's safe to compare the versions with
  # sort -V
  if [ "${va}" = "${vaMMPB}" ] && [ "${vb}" = "${vbMMPB}" ]; then
    { version_gt "${@}" && return 1; } || return 255
  fi

  # If the MAJOR.MINOR.PATCH.BUILD strings are equal at this point, it means
  # that one of the two semvers has a suffix, and a suffixless semver is treated
  # as greater than one with a suffix. 
  if [ "${vaMMPB}" = "${vbMMPB}" ]; then
    if [ "${va}" = "${vaMMPB}" ] && [ ! "${vb}" = "${vbMMPB}" ]; then
      return 1
    elif [ ! "${va}" = "${vaMMPB}" ] && [ "${vb}" = "${vbMMPB}" ]; then
      return 255
    else
      { version_gt "${@}" && return 1; } || return 255
    fi
  fi

  # At this point it's known that the MAJOR.MINOR.PATCH.BUILD strings are not
  # equal, and thus it is safe to compare the two versions using sort -V.
  { version_gt "${@}" && return 1; } || return 255
}

[ -z "${TEST_SEMVER_COMP}" ] && { semver_comp "${@}"; exit "${?}"; }

printf '% 15s % 15s % 5s % 5s\n' 'a' 'b' 'exp' 'act'
test_semver_comp() {
  set +e
  semver_comp "${1}" "${2}"; result="${?}"
  set -e
  printf '% 15s % 15s % 5d % 5d\n' \
    "${1}" "${2}" "${3}" "${result}"
  test "${result}" -eq "${3}"
}

test_semver_comp v1.0 v1.0 0
test_semver_comp v10.0 v1.0 1
test_semver_comp v1.0 v10.0 255
test_semver_comp v1.14 v1.14.alpha1 1
test_semver_comp v1.14.alpha1 v1.14 255
test_semver_comp v1.140.alpha1 v1.14 1

exit 0