diff --git a/libexec/rbenv-completions b/libexec/rbenv-completions
index 6de09ed2..196212e4 100755
--- a/libexec/rbenv-completions
+++ b/libexec/rbenv-completions
@@ -11,7 +11,7 @@ if [ -z "$COMMAND" ]; then
 fi
 
 COMMAND_PATH="$(command -v "rbenv-$COMMAND" || command -v "rbenv-sh-$COMMAND")"
-if grep -i "^\([#%]\|--\|//\) provide rbenv completions" "$COMMAND_PATH" >/dev/null; then
+if grep -iE "^([#%]|--|//) provide rbenv completions" "$COMMAND_PATH" >/dev/null; then
   shift
   exec "$COMMAND_PATH" --complete "$@"
 fi
diff --git a/libexec/rbenv-init b/libexec/rbenv-init
index a3292d66..a28b7fc4 100755
--- a/libexec/rbenv-init
+++ b/libexec/rbenv-init
@@ -22,8 +22,9 @@ done
 
 shell="$1"
 if [ -z "$shell" ]; then
-  shell="$(ps c -p $(ps -p $$ -o 'ppid=' 2>/dev/null) -o 'comm=' 2>/dev/null || true)"
+  shell="$(ps c -p "$PPID" -o 'ucomm=' 2>/dev/null || true)"
   shell="${shell##-}"
+  shell="${shell%% *}"
   shell="$(basename "${shell:-$SHELL}")"
 fi
 
diff --git a/test/completions.bats b/test/completions.bats
index 0feccfa9..9091f082 100644
--- a/test/completions.bats
+++ b/test/completions.bats
@@ -18,7 +18,7 @@ create_command() {
 
 @test "command with completion support" {
   create_command "rbenv-hello" "#!$BASH
-# provide rbenv completions
+# Provide rbenv completions
 if [[ \$1 = --complete ]]; then
   echo hello
 else
diff --git a/test/init.bats b/test/init.bats
index 61b30be7..60a3328c 100644
--- a/test/init.bats
+++ b/test/init.bats
@@ -51,14 +51,14 @@ load test_helper
 }
 
 @test "adds shims to PATH" {
-  export PATH="${BATS_TEST_DIRNAME}/../libexec:/usr/bin:/bin"
+  export PATH="${BATS_TEST_DIRNAME}/../libexec:/usr/bin:/bin:/usr/local/bin"
   run rbenv-init - bash
   assert_success
   assert_line 0 'export PATH="'${RBENV_ROOT}'/shims:${PATH}"'
 }
 
 @test "adds shims to PATH (fish)" {
-  export PATH="${BATS_TEST_DIRNAME}/../libexec:/usr/bin:/bin"
+  export PATH="${BATS_TEST_DIRNAME}/../libexec:/usr/bin:/bin:/usr/local/bin"
   run rbenv-init - fish
   assert_success
   assert_line 0 "setenv PATH '${RBENV_ROOT}/shims' \$PATH"
diff --git a/test/prefix.bats b/test/prefix.bats
index 0d6cdba6..3fb94086 100644
--- a/test/prefix.bats
+++ b/test/prefix.bats
@@ -25,15 +25,6 @@ load test_helper
 }
 
 @test "prefix for invalid system" {
-  USRBIN_ALT="${RBENV_TEST_DIR}/usr-bin-alt"
-  mkdir -p "$USRBIN_ALT"
-  for util in head readlink greadlink; do
-    if [ -x "/usr/bin/$util" ]; then
-      ln -s "/usr/bin/$util" "${USRBIN_ALT}/$util"
-    fi
-  done
-  PATH_WITHOUT_RUBY="${PATH/\/usr\/bin:/$USRBIN_ALT:}"
-
-  PATH="$PATH_WITHOUT_RUBY" run rbenv-prefix system
+  PATH="$(path_without ruby)" run rbenv-prefix system
   assert_failure "rbenv: system version not found in PATH"
 }
diff --git a/test/test_helper.bash b/test/test_helper.bash
index 01d9fb99..53ae8e64 100644
--- a/test/test_helper.bash
+++ b/test/test_helper.bash
@@ -8,7 +8,7 @@ if [ "$RBENV_ROOT" != "${RBENV_TEST_DIR}/root" ]; then
   export RBENV_ROOT="${RBENV_TEST_DIR}/root"
   export HOME="${RBENV_TEST_DIR}/home"
 
-  PATH=/usr/bin:/bin:/usr/sbin:/sbin
+  PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
   PATH="${RBENV_TEST_DIR}/bin:$PATH"
   PATH="${BATS_TEST_DIRNAME}/../libexec:$PATH"
   PATH="${BATS_TEST_DIRNAME}/libexec:$PATH"
@@ -93,3 +93,25 @@ assert() {
     flunk "failed: $@"
   fi
 }
+
+# Output a modified PATH that ensures that the given executable is not present,
+# but in which system utils necessary for rbenv operation are still available.
+path_without() {
+  local exe="$1"
+  local path="${PATH}:"
+  local found alt util
+  for found in $(which -a "$exe"); do
+    found="${found%/*}"
+    if [ "$found" != "${RBENV_ROOT}/shims" ]; then
+      alt="${RBENV_TEST_DIR}/$(echo "${found#/}" | tr '/' '-')"
+      mkdir -p "$alt"
+      for util in bash head cut readlink greadlink; do
+        if [ -x "${found}/$util" ]; then
+          ln -s "${found}/$util" "${alt}/$util"
+        fi
+      done
+      path="${path/${found}:/${alt}:}"
+    fi
+  done
+  echo "${path%:}"
+}