Add `nvm_get_minor_version`

nvm.sh

@@ -995,6 +995,34 @@ nvm_get_arch() {
   echo "$NVM_ARCH"
 }
 
+nvm_get_minor_version() {
+  local VERSION
+  VERSION="$1"
+
+  if [ -z "$VERSION" ]; then
+    echo 'a version is required' >&2
+    return 1
+  fi
+
+  case "$VERSION" in
+    v | .* | *..* | v*[!.0123456789]* | [!v]*[!.0123456789]* | [!v0123456789]* | v[!0123456789]*)
+      echo 'invalid version number' >&2
+      return 2
+    ;;
+  esac
+
+  local PREFIXED_VERSION
+  PREFIXED_VERSION="$(nvm_format_version "$VERSION")"
+
+  local MINOR
+  MINOR="$(echo "$PREFIXED_VERSION" | command grep -e '^v' | command cut -c2- | command cut -d . -f 1,2)"
+  if [ -z "$MINOR" ]; then
+    echo 'invalid version number! (please report this)' >&2
+    return 3
+  fi
+  echo "$MINOR"
+}
+
 nvm_ensure_default_set() {
   local VERSION
   VERSION="$1"

test/fast/Unit tests/nvm_get_minor_version

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+expect () {
+  INPUT="$1"
+  EXPECTED_OUTPUT="$2"
+
+  OUTPUT="$(nvm_get_minor_version "$INPUT")"
+  [ "_$OUTPUT" = "_$EXPECTED_OUTPUT" ] || die "nvm_get_minor_version $INPUT did not return $EXPECTED_OUTPUT; got $OUTPUT"
+
+  V_OUTPUT="$(nvm_get_minor_version "v$INPUT")"
+  [ "_$V_OUTPUT" = "_$EXPECTED_OUTPUT" ] || die "nvm_get_minor_version v$INPUT did not return $EXPECTED_OUTPUT; got $V_OUTPUT"
+}
+
+fail_with () {
+  INPUT="$1"
+  EXPECTED_CODE="$2"
+
+  EXIT_CODE="$(nvm_get_minor_version "$INPUT" >/dev/null 2>&1; echo $?)"
+  [ "_$EXIT_CODE" = "_$EXPECTED_CODE" ] || die "nvm_get_minor_version "$INPUT" did not fail with code "$EXPECTED_CODE"; got $EXIT_CODE"
+}
+
+expect 1 1.0
+expect 1. 1.0
+expect 1.2 1.2
+expect 1.2. 1.2
+expect 1.2.3 1.2
+expect 1.2.3. 1.2
+expect 1.2.3.4 1.2
+
+fail_with '' 1
+fail_with '.' 2
+fail_with '..' 2
+fail_with v 2
+fail_with .a 2
+fail_with .1 2
+fail_with v.1 2
+fail_with a.b 2
+fail_with 1.a 2
+fail_with a.1 2
+fail_with v1.a 2
+fail_with va.1 2