diff --git a/_build.sh b/_build.sh
index 040cd370e..791d7a95d 100755
--- a/_build.sh
+++ b/_build.sh
@@ -208,13 +208,13 @@ my_time='time'
 [ -n "${CW_NOTIME:-}" ] && my_time=
 
 # Detect host OS
-export _OS
+export _HOSTOS
 case "$(uname)" in
-  *_NT*)   _OS='win';;
-  Linux*)  _OS='linux';;
-  Darwin*) _OS='mac';;
-  *BSD)    _OS='bsd';;
-  *)       _OS='unrecognized';;
+  *_NT*)   _HOSTOS='win';;
+  Linux*)  _HOSTOS='linux';;
+  Darwin*) _HOSTOS='mac';;
+  *BSD)    _HOSTOS='bsd';;
+  *)       _HOSTOS='unrecognized';;
 esac
 
 # Form suffix for alternate builds
@@ -238,7 +238,7 @@ fi
 #    `configure: WARNING: using cross tools not prefixed with host triplet`
 # Even with `_CCPREFIX` provided.
 # https://clang.llvm.org/docs/CrossCompilation.html
-case "${_OS}" in
+case "${_HOSTOS}" in
   win)   _BUILD_HOST="${unamem}-pc-mingw32";;
   linux) _BUILD_HOST="${unamem}-pc-linux";;
   bsd)   _BUILD_HOST="${unamem}-pc-bsd";;
@@ -271,7 +271,7 @@ export _REVSUFFIX="${_REV}"; [ -z "${_REVSUFFIX}" ] || _REVSUFFIX="_${_REVSUFFIX
 . ./_dl.sh
 
 # Install required component
-if [ "${_OS}" = 'mac' ]; then
+if [ "${_HOSTOS}" = 'mac' ]; then
   if [ ! -d .venv ]; then
     python3 -m venv .venv
     PIP_PROGRESS_BAR=off .venv/bin/python3 -m pip --disable-pip-version-check --no-cache-dir --require-virtualenv install pefile
@@ -433,7 +433,7 @@ build_single_target() {
   # Reset for each target
   PATH="${_ori_path}"
 
-  if [ "${_OS}" = 'win' ]; then
+  if [ "${_HOSTOS}" = 'win' ]; then
     export PATH
     if [ "${_TOOLCHAIN}" = 'llvm-mingw' ]; then
       PATH="${CW_LLVM_MINGW_PATH}/bin:${_ori_path}"
@@ -448,7 +448,7 @@ build_single_target() {
   else
     if [ "${_TOOLCHAIN}" = 'llvm-mingw' ]; then
       export PATH="${CW_LLVM_MINGW_PATH}/bin:${_ori_path}"
-    elif [ "${_CC}" = 'llvm' ] && [ "${_OS}" = 'mac' ]; then
+    elif [ "${_CC}" = 'llvm' ] && [ "${_HOSTOS}" = 'mac' ]; then
       _MAC_LLVM_PATH='/usr/local/opt/llvm/bin'
       export PATH="${_MAC_LLVM_PATH}:${_ori_path}"
     fi
@@ -459,16 +459,16 @@ build_single_target() {
     _CCPREFIX="${_TRIPLET}-"
     # mingw-w64 sysroots
     if [ "${_TOOLCHAIN}" != 'llvm-mingw' ]; then
-      if [ "${_OS}" = 'mac' ]; then
+      if [ "${_HOSTOS}" = 'mac' ]; then
         _SYSROOT="/usr/local/opt/mingw-w64/toolchain-${_machine}"
-      elif [ "${_OS}" = 'linux' ]; then
+      elif [ "${_HOSTOS}" = 'linux' ]; then
         _SYSROOT="/usr/${_TRIPLET}"
       fi
     fi
 
     _WINE='echo'
-    if [ "${_OS}" = 'linux' ] || \
-       [ "${_OS}" = 'bsd' ]; then
+    if [ "${_HOSTOS}" = 'linux' ] || \
+       [ "${_HOSTOS}" = 'bsd' ]; then
       # Run x64 targets on same CPU:
       if [ "${_CPU}" = 'x64' ] && \
          [ "${unamem}" = 'x86_64' ]; then
@@ -478,13 +478,13 @@ build_single_target() {
           _WINE='wine'
         fi
       fi
-    elif [ "${_OS}" = 'mac' ]; then
+    elif [ "${_HOSTOS}" = 'mac' ]; then
       # Run x64 targets on Intel and ARM (requires Wine 6.0.1):
       if [ "${_CPU}" = 'x64' ] && \
          command -v wine64 >/dev/null 2>&1; then
         _WINE='wine64'
       fi
-    elif [ "${_OS}" = 'win' ]; then
+    elif [ "${_HOSTOS}" = 'win' ]; then
       # Skip ARM64 target on 64-bit Intel, run all targets on ARM64:
       if [ "${unamem}" = 'x86_64' ] && \
          [ "${_CPU}" != 'a64' ]; then
@@ -545,7 +545,7 @@ build_single_target() {
   [ "${_CPU}" = 'x64' ] && _RCFLAGS_GLOBAL="${_RCFLAGS_GLOBAL} --target=pe-x86-64"
   [ "${_CPU}" = 'a64' ] && _RCFLAGS_GLOBAL="${_RCFLAGS_GLOBAL} --target=${_TRIPLET}"  # llvm-windres supports triplets here. https://github.com/llvm/llvm-project/blob/main/llvm/tools/llvm-rc/llvm-rc.cpp
 
-  if [ "${_OS}" = 'win' ]; then
+  if [ "${_HOSTOS}" = 'win' ]; then
     # '-G MSYS Makefiles' command-line option is problematic due to spaces
     # and unwanted escaping/splitting. Pass it via envvar instead.
     export CMAKE_GENERATOR='MSYS Makefiles'
@@ -577,7 +577,7 @@ build_single_target() {
       _CC_GLOBAL="${_CC_GLOBAL} --sysroot=${_SYSROOT}"
       _CONFIGURE_GLOBAL="${_CONFIGURE_GLOBAL} --with-sysroot=${_SYSROOT}"
     fi
-    if [ "${_OS}" = 'linux' ]; then
+    if [ "${_HOSTOS}" = 'linux' ]; then
       # We used to pass this via CFLAGS for CMake to make it detect llvm/clang,
       # so we need to pass this via CMAKE_C_FLAGS, though meant for the linker.
       if [ "${_TOOLCHAIN}" = 'llvm-mingw' ]; then
@@ -634,7 +634,7 @@ build_single_target() {
       _BINUTILS_PREFIX='llvm-'
       _BINUTILS_SUFFIX="${_CCSUFFIX}"
       _LDFLAGS_GLOBAL="${_LDFLAGS_GLOBAL} -fuse-ld=lld${_CCSUFFIX}"
-      if [ "${_OS}" = 'mac' ]; then
+      if [ "${_HOSTOS}" = 'mac' ]; then
         _RCFLAGS_GLOBAL="${_RCFLAGS_GLOBAL} -I${_SYSROOT}/${_TRIPLET}/include"
       fi
     fi
@@ -698,7 +698,7 @@ build_single_target() {
   export RC="${_BINUTILS_PREFIX}windres${_BINUTILS_SUFFIX}"
   if [ "${_CC}" = 'llvm' ] && \
      [ "${_TOOLCHAIN}" != 'llvm-mingw' ] && \
-     [ "${_OS}" = 'linux' ] && \
+     [ "${_HOSTOS}" = 'linux' ] && \
      [ -n "${_BINUTILS_SUFFIX}" ]; then
     # FIXME: llvm-windres present, but unable to find its clang counterpart
     #        when suffixed:
@@ -734,7 +734,7 @@ build_single_target() {
     chmod +x "${AR_NORMALIZE}"
   fi
 
-  if [ "${_OS}" = 'mac' ]; then
+  if [ "${_HOSTOS}" = 'mac' ]; then
     if [ "${_TOOLCHAIN}" = 'llvm-mingw' ]; then
       _CMAKE_GLOBAL="${_CMAKE_GLOBAL} -DCMAKE_AR=${CW_LLVM_MINGW_PATH}/bin/${AR}"
     elif [ "${_CC}" = 'llvm' ]; then
@@ -776,7 +776,7 @@ build_single_target() {
     mingwver="${mingwver} ${CW_LLVM_MINGW_VER_:-?}"
     versuffix="${versuffix_llvm_mingw}"
   else
-    case "${_OS}" in
+    case "${_HOSTOS}" in
       mac)
         mingwver="$(HOMEBREW_NO_AUTO_UPDATE=1 HOMEBREW_NO_INSTALL_FROM_API=1 brew info --json=v2 --formula mingw-w64 | jq --raw-output '.formulae[] | select(.name == "mingw-w64") | .versions.stable')";;
       linux)
@@ -908,7 +908,7 @@ if [ "${_BRANCH#*x64*}" = "${_BRANCH}" ] && \
   build_single_target x86
 fi
 
-case "${_OS}" in
+case "${_HOSTOS}" in
   mac)   rm -f -P "${SIGN_CODE_KEY}";;
   linux) [ -w "${SIGN_CODE_KEY}" ] && srm "${SIGN_CODE_KEY}";;
 esac
diff --git a/_dl.sh b/_dl.sh
index 578f42c30..4981f509a 100755
--- a/_dl.sh
+++ b/_dl.sh
@@ -527,7 +527,7 @@ echo "Build: REV(${_REVSUFFIX})"
 # Quit if any of the lines fail
 set -e
 
-if [ "${_OS}" = 'mac' ]; then
+if [ "${_HOSTOS}" = 'mac' ]; then
   tar() { gtar "$@"; }
 fi
 
@@ -631,13 +631,13 @@ EOF
 if [ "${CW_LLVM_MINGW_DL:-}" = '1' ] && \
    [ ! -d 'llvm-mingw' ]; then
   name=''; vers=''; hash=''; arch="$(uname -m)"
-  if   [ "${_OS}-${arch}" = 'linux-x86_64' ]; then
+  if   [ "${_HOSTOS}-${arch}" = 'linux-x86_64' ]; then
     name='llvm-mingw-linux-x86-64'; vers="${LLVM_MINGW_LINUX_X86_64_VER_}"; hash="${LLVM_MINGW_LINUX_X86_64_HASH}"
-  elif [ "${_OS}-${arch}" = 'linux-aarch64' ]; then
+  elif [ "${_HOSTOS}-${arch}" = 'linux-aarch64' ]; then
     name='llvm-mingw-linux-aarch64'; vers="${LLVM_MINGW_LINUX_AARCH64_VER_}"; hash="${LLVM_MINGW_LINUX_AARCH64_HASH}"
-  elif [ "${_OS}" = 'mac' ]; then
+  elif [ "${_HOSTOS}" = 'mac' ]; then
     name='llvm-mingw-mac';   vers="${LLVM_MINGW_MAC_VER_}";   hash="${LLVM_MINGW_MAC_HASH}"
-  elif [ "${_OS}" = 'win' ]; then
+  elif [ "${_HOSTOS}" = 'win' ]; then
     name='llvm-mingw-win';   vers="${LLVM_MINGW_WIN_VER_}";   hash="${LLVM_MINGW_WIN_HASH}"
   fi
   if [ -n "${name}" ]; then
diff --git a/_pkg.sh b/_pkg.sh
index 52dffb41e..3a278b149 100755
--- a/_pkg.sh
+++ b/_pkg.sh
@@ -8,7 +8,7 @@ set -o xtrace -o errexit -o nounset; [ -n "${BASH:-}${ZSH_NAME:-}" ] && set -o p
 
 cd "$(dirname "$0")"
 
-if [ "${_OS}" = 'mac' ]; then
+if [ "${_HOSTOS}" = 'mac' ]; then
   tar() { gtar "$@"; }
 fi
 
@@ -53,11 +53,11 @@ create_pkg() {
   fi
   # Alter filename for non-release packages
   if [ "${_BRANCH#*main*}" != "${_BRANCH}" ]; then
-    if [ "${PUBLISH_PROD_FROM}" != "${_OS}" ]; then
-      _suf="${_suf}-built-on-${_OS}"
+    if [ "${PUBLISH_PROD_FROM}" != "${_HOSTOS}" ]; then
+      _suf="${_suf}-built-on-${_HOSTOS}"
     fi
   else
-    _suf="${_suf}-test-built-on-${_OS}"
+    _suf="${_suf}-test-built-on-${_HOSTOS}"
   fi
 
   _pkg="${_OUT}${_suf}${arch_ext}"
@@ -66,7 +66,7 @@ create_pkg() {
 
   (
     cd "${_DST}/.."
-    case "${_OS}" in
+    case "${_HOSTOS}" in
       win) find "${_BAS}" -exec attrib +A -R '{}' \;
     esac
 
@@ -87,7 +87,7 @@ create_pkg() {
   rm -f "${_FLS}"
 
   # <filename>: <size> bytes <YYYY-MM-DD> <HH:MM>
-  case "${_OS}" in
+  case "${_HOSTOS}" in
     bsd|mac) TZ=UTC stat -f '%N: %z bytes %Sm' -t '%Y-%m-%d %H:%M' "${_pkg}";;
     *)       TZ=UTC stat --format='%n: %s bytes %y' "${_pkg}";;
   esac
diff --git a/_sign-code.sh b/_sign-code.sh
index 40e37264a..ed3cffdb9 100755
--- a/_sign-code.sh
+++ b/_sign-code.sh
@@ -12,7 +12,7 @@ if [ -s "${SIGN_CODE_KEY}" ] && \
   _ref="$1"
   shift
 
-  case "${_OS}" in
+  case "${_HOSTOS}" in
     bsd|mac) unixts="$(TZ=UTC stat -f '%m' "${_ref}")";;
     *)       unixts="$(TZ=UTC stat --format='%Y' "${_ref}")";;
   esac
diff --git a/_ul.sh b/_ul.sh
index fc3d27de4..0d8c8027b 100755
--- a/_ul.sh
+++ b/_ul.sh
@@ -55,7 +55,7 @@ touch -c -r "${_ALL}" "${_ALL}.txt"
 
 # Official deploy
 DEPLOY_KEY="$(realpath '.')/deploy.key"
-if [ "${PUBLISH_PROD_FROM}" = "${_OS}" ] && \
+if [ "${PUBLISH_PROD_FROM}" = "${_HOSTOS}" ] && \
    [ "${_BRANCH#*main*}" != "${_BRANCH}" ] && \
    [ -s "${DEPLOY_KEY}.asc" ] && \
    [ -n "${DEPLOY_GPG_PASS:+1}" ]; then
@@ -107,7 +107,7 @@ EOF
       'curl-for-win@silly.haxx.se:.'
   fi
 
-  case "${_OS}" in
+  case "${_HOSTOS}" in
     mac)   rm -f -P "${DEPLOY_KEY}";;
     linux) [ -w "${DEPLOY_KEY}" ] && srm "${DEPLOY_KEY}";;
   esac
diff --git a/curl-pkg.sh b/curl-pkg.sh
index a94068d18..3b6f4572c 100755
--- a/curl-pkg.sh
+++ b/curl-pkg.sh
@@ -35,7 +35,7 @@
   # Tests
 
   # Show the reference timestamp in UTC.
-  case "${_OS}" in
+  case "${_HOSTOS}" in
     bsd|mac) TZ=UTC stat -f '%N: %Sm' -t '%Y-%m-%d %H:%M' "${_ref}";;
     *)       TZ=UTC stat --format='%n: %y' "${_ref}";;
   esac
diff --git a/openssl.sh b/openssl.sh
index 3a608fe81..21b3d8ab0 100755
--- a/openssl.sh
+++ b/openssl.sh
@@ -15,11 +15,11 @@ _VER="$1"
   cd "${_NAM}" || exit 0
 
   # Required on MSYS2 for pod2man and pod2html in 'make install' phase
-  [ "${_OS}" = 'win' ] && export PATH="${PATH}:/usr/bin/core_perl"
+  [ "${_HOSTOS}" = 'win' ] && export PATH="${PATH}:/usr/bin/core_perl"
 
   readonly _ref='CHANGES.md'
 
-  case "${_OS}" in
+  case "${_HOSTOS}" in
     bsd|mac) unixts="$(TZ=UTC stat -f '%m' "${_ref}")";;
     *)       unixts="$(TZ=UTC stat --format='%Y' "${_ref}")";;
   esac