diff --git a/Library/Homebrew/cmd/shellenv.sh b/Library/Homebrew/cmd/shellenv.sh
index 5c27621515..8dc8b98fb0 100644
--- a/Library/Homebrew/cmd/shellenv.sh
+++ b/Library/Homebrew/cmd/shellenv.sh
@@ -3,15 +3,15 @@
 #:  Print export statements. When run in a shell, this installation of Homebrew will be added to your `PATH`, `MANPATH`, and `INFOPATH`.
 #:
 #:  The variables `HOMEBREW_PREFIX`, `HOMEBREW_CELLAR` and `HOMEBREW_REPOSITORY` are also exported to avoid querying them multiple times.
-#:  The variable `HOMEBREW_SHELLENV_PREFIX` will be exported to avoid adding duplicate entries to the environment variables.
-#:  Consider adding evaluation of this command's output to your dotfiles (e.g. `~/.profile`, `~/.bash_profile`, or `~/.zprofile`) with: `eval "$(brew shellenv)"`
+#:  To help guarantee idempotence, this command produces no output when Homebrew's `bin` and `sbin` directores are first and second
+#:  respectively in your `PATH`. Consider adding evaluation of this command's output to your dotfiles (e.g. `~/.profile`,
+#:  `~/.bash_profile`, or `~/.zprofile`) with: `eval "$(brew shellenv)"`
 
 # HOMEBREW_CELLAR and HOMEBREW_PREFIX are set by extend/ENV/super.rb
 # HOMEBREW_REPOSITORY is set by bin/brew
 # shellcheck disable=SC2154
 homebrew-shellenv() {
-  if [[ "${HOMEBREW_SHELLENV_PREFIX}" == "${HOMEBREW_PREFIX}" ]] &&
-     [[ "$(PATH="${HOMEBREW_PATH}" command -v brew)" == "${HOMEBREW_PREFIX}/bin/brew" ]]
+  if [[ "${HOMEBREW_PATH%%:"${HOMEBREW_PREFIX}"/sbin*}" == "${HOMEBREW_PREFIX}/bin" ]]
   then
     return
   fi
@@ -21,7 +21,6 @@ homebrew-shellenv() {
       echo "set -gx HOMEBREW_PREFIX \"${HOMEBREW_PREFIX}\";"
       echo "set -gx HOMEBREW_CELLAR \"${HOMEBREW_CELLAR}\";"
       echo "set -gx HOMEBREW_REPOSITORY \"${HOMEBREW_REPOSITORY}\";"
-      echo "set -gx HOMEBREW_SHELLENV_PREFIX \"${HOMEBREW_PREFIX}\";"
       echo "set -q PATH; or set PATH ''; set -gx PATH \"${HOMEBREW_PREFIX}/bin\" \"${HOMEBREW_PREFIX}/sbin\" \$PATH;"
       echo "set -q MANPATH; or set MANPATH ''; set -gx MANPATH \"${HOMEBREW_PREFIX}/share/man\" \$MANPATH;"
       echo "set -q INFOPATH; or set INFOPATH ''; set -gx INFOPATH \"${HOMEBREW_PREFIX}/share/info\" \$INFOPATH;"
@@ -30,7 +29,6 @@ homebrew-shellenv() {
       echo "setenv HOMEBREW_PREFIX ${HOMEBREW_PREFIX};"
       echo "setenv HOMEBREW_CELLAR ${HOMEBREW_CELLAR};"
       echo "setenv HOMEBREW_REPOSITORY ${HOMEBREW_REPOSITORY};"
-      echo "setenv HOMEBREW_SHELLENV_PREFIX ${HOMEBREW_PREFIX};"
       echo "setenv PATH ${HOMEBREW_PREFIX}/bin:${HOMEBREW_PREFIX}/sbin:\$PATH;"
       echo "setenv MANPATH ${HOMEBREW_PREFIX}/share/man\`[ \${?MANPATH} == 1 ] && echo \":\${MANPATH}\"\`:;"
       echo "setenv INFOPATH ${HOMEBREW_PREFIX}/share/info\`[ \${?INFOPATH} == 1 ] && echo \":\${INFOPATH}\"\`;"
@@ -39,7 +37,6 @@ homebrew-shellenv() {
       echo "[System.Environment]::SetEnvironmentVariable('HOMEBREW_PREFIX','${HOMEBREW_PREFIX}',[System.EnvironmentVariableTarget]::Process)"
       echo "[System.Environment]::SetEnvironmentVariable('HOMEBREW_CELLAR','${HOMEBREW_CELLAR}',[System.EnvironmentVariableTarget]::Process)"
       echo "[System.Environment]::SetEnvironmentVariable('HOMEBREW_REPOSITORY','${HOMEBREW_REPOSITORY}',[System.EnvironmentVariableTarget]::Process)"
-      echo "[System.Environment]::SetEnvironmentVariable('HOMEBREW_SHELLENV_PREFIX','${HOMEBREW_PREFIX}',[System.EnvironmentVariableTarget]::Process)"
       echo "[System.Environment]::SetEnvironmentVariable('PATH',\$('${HOMEBREW_PREFIX}/bin:${HOMEBREW_PREFIX}/sbin:'+\$ENV:PATH),[System.EnvironmentVariableTarget]::Process)"
       echo "[System.Environment]::SetEnvironmentVariable('MANPATH',\$('${HOMEBREW_PREFIX}/share/man'+\$(if(\${ENV:MANPATH}){':'+\${ENV:MANPATH}})+':'),[System.EnvironmentVariableTarget]::Process)"
       echo "[System.Environment]::SetEnvironmentVariable('INFOPATH',\$('${HOMEBREW_PREFIX}/share/info'+\$(if(\${ENV:INFOPATH}){':'+\${ENV:INFOPATH}})),[System.EnvironmentVariableTarget]::Process)"
@@ -48,7 +45,6 @@ homebrew-shellenv() {
       echo "export HOMEBREW_PREFIX=\"${HOMEBREW_PREFIX}\";"
       echo "export HOMEBREW_CELLAR=\"${HOMEBREW_CELLAR}\";"
       echo "export HOMEBREW_REPOSITORY=\"${HOMEBREW_REPOSITORY}\";"
-      echo "export HOMEBREW_SHELLENV_PREFIX=\"${HOMEBREW_PREFIX}\";"
       echo "export PATH=\"${HOMEBREW_PREFIX}/bin:${HOMEBREW_PREFIX}/sbin\${PATH+:\$PATH}\";"
       echo "export MANPATH=\"${HOMEBREW_PREFIX}/share/man\${MANPATH+:\$MANPATH}:\";"
       echo "export INFOPATH=\"${HOMEBREW_PREFIX}/share/info:\${INFOPATH:-}\";"