brew.sh: avoid shelling out when possible.

Library/Homebrew/brew.sh

@@ -3,16 +3,33 @@
 ##### to be able to `source` in shell configurations run quickly.
 #####
 
-# Doesn't need a default case because we don't support other OSs
+case "${MACHTYPE}" in
-# shellcheck disable=SC2249
+  arm64-*)
+    HOMEBREW_PROCESSOR="arm64"
+    ;;
+  x86_64-*)
+    HOMEBREW_PROCESSOR="x86_64"
+    ;;
+  *)
     HOMEBREW_PROCESSOR="$(uname -m)"
-HOMEBREW_PHYSICAL_PROCESSOR="${HOMEBREW_PROCESSOR}"
+    ;;
-HOMEBREW_SYSTEM="$(uname -s)"
-case "${HOMEBREW_SYSTEM}" in
-  Darwin) HOMEBREW_MACOS="1" ;;
-  Linux) HOMEBREW_LINUX="1" ;;
 esac
 
+case "${OSTYPE}" in
+  darwin*)
+    HOMEBREW_SYSTEM="Darwin"
+    HOMEBREW_MACOS="1"
+    ;;
+  linux*)
+    HOMEBREW_SYSTEM="Linux"
+    HOMEBREW_LINUX="1"
+    ;;
+  *)
+    HOMEBREW_SYSTEM="$(uname -s)"
+    ;;
+esac
+HOMEBREW_PHYSICAL_PROCESSOR="${HOMEBREW_PROCESSOR}"
+
 HOMEBREW_MACOS_ARM_DEFAULT_PREFIX="/opt/homebrew"
 HOMEBREW_MACOS_ARM_DEFAULT_REPOSITORY="${HOMEBREW_MACOS_ARM_DEFAULT_PREFIX}"
 HOMEBREW_LINUX_DEFAULT_PREFIX="/home/linuxbrew/.linuxbrew"
@@ -79,11 +96,11 @@ HOMEBREW_CACHE="${HOMEBREW_CACHE:-${HOMEBREW_DEFAULT_CACHE}}"
 HOMEBREW_LOGS="${HOMEBREW_LOGS:-${HOMEBREW_DEFAULT_LOGS}}"
 HOMEBREW_TEMP="${HOMEBREW_TEMP:-${HOMEBREW_DEFAULT_TEMP}}"
 
-# Don't need to handle a default case.
-# HOMEBREW_LIBRARY set by bin/brew
-# shellcheck disable=SC2249,SC2154
-#
 # commands that take a single or no arguments.
+# HOMEBREW_LIBRARY set by bin/brew
+# shellcheck disable=SC2154
+# doesn't need a default case as other arguments handled elsewhere.
+# shellcheck disable=SC2249
 case "$1" in
   formulae)
     source "${HOMEBREW_LIBRARY}/Homebrew/cmd/formulae.sh"
@@ -109,6 +126,8 @@ case "$1" in
     ;;
 esac
 # functions that take multiple arguments or handle multiple commands.
+# doesn't need a default case as other arguments handled elsewhere.
+# shellcheck disable=SC2249
 case "$@" in
   --cellar)
     echo "${HOMEBREW_CELLAR}"
@@ -232,7 +251,7 @@ numeric() {
 }
 
 check-run-command-as-root() {
-  [[ "$(id -u)" == 0 || "$(id -ur)" == 0 ]] || return
+  [[ "${EUID}" == 0 || "${UID}" == 0 ]] || return
 
   # Allow Azure Pipelines/GitHub Actions/Docker/Concourse/Kubernetes to do everything as root (as it's normal there)
   [[ -f /.dockerenv ]] && return
@@ -429,11 +448,11 @@ fi
 
 # Many Pathname operations use getwd when they shouldn't, and then throw
 # odd exceptions. Reduce our support burden by showing a user-friendly error.
-if ! [[ -d "$(pwd)" ]]
+if ! [[ -d "${PWD}" ]]
 then
   odie "The current working directory must exist to run brew."
 fi
-if ! [[ -r "$(pwd)" ]]
+if ! [[ -r "${PWD}" ]]
 then
   odie "The current working directory must be readable to ${USER} to run brew."
 fi
@@ -536,6 +555,8 @@ then
 fi
 
 # commands that take a single or no arguments.
+# doesn't need a default case as other arguments handled elsewhere.
+# shellcheck disable=SC2249
 case "$1" in
   --version | -v)
     source "${HOMEBREW_LIBRARY}/Homebrew/cmd/--version.sh"
@@ -807,6 +828,7 @@ EOS
   # a popup window asking the user to install the CLT
   if [[ -n "${XCODE_SELECT_PATH}" ]]
   then
+    # TODO: this is fairly slow, figure out if there's a faster way.
     XCRUN_OUTPUT="$(/usr/bin/xcrun clang 2>&1)"
     XCRUN_STATUS="$?"
 
@@ -836,6 +858,8 @@ HOMEBREW_COMMAND="$1"
 shift
 # If you are going to change anything in below case statement,
 # be sure to also update HOMEBREW_INTERNAL_COMMAND_ALIASES hash in commands.rb
+# doesn't need a default case as other arguments handled elsewhere.
+# shellcheck disable=SC2249
 case "${HOMEBREW_COMMAND}" in
   ls) HOMEBREW_COMMAND="list" ;;
   homepage) HOMEBREW_COMMAND="home" ;;