diff --git a/.travis/setup_lua.sh b/.travis/setup_lua.sh
index b040508..00830bc 100644
--- a/.travis/setup_lua.sh
+++ b/.travis/setup_lua.sh
@@ -1,6 +1,5 @@
 #! /bin/bash
-
-# vim: ft=bash sw=2 ts=2
+# vim: ft=sh sw=2 ts=2
 
 # A script for setting up environment for travis-ci testing.
 # Sets up Lua and Luarocks.
@@ -11,112 +10,99 @@
 set -eufo pipefail
 
 LUAJIT_VERSION="2.0.5"
-LUAJIT_BASE="LuaJIT-$LUAJIT_VERSION"
+LUAJIT_BASE="LuaJIT-${LUAJIT_VERSION}"
 
+# shellcheck disable=SC1091
 source .travis/platform.sh
 
-LUA_HOME_DIR=$TRAVIS_BUILD_DIR/install/lua
+LUA_HOME_DIR="${TRAVIS_BUILD_DIR}/install/lua"
 
-LR_HOME_DIR=$TRAVIS_BUILD_DIR/install/luarocks
+LR_HOME_DIR="${TRAVIS_BUILD_DIR}/install/luarocks"
 
-mkdir $HOME/.lua
+mkdir "${HOME}/.lua" -p
 
 LUAJIT="no"
 
-if [ "$PLATFORM" == "macosx" ]; then
-  if [ "$LUA" == "luajit" ]; then
-    LUAJIT="yes";
-  fi
-  if [ "$LUA" == "luajit2.0" ]; then
-    LUAJIT="yes";
-  fi
-  if [ "$LUA" == "luajit2.1" ]; then
-    LUAJIT="yes";
-  fi;
-elif [ "$(expr substr $LUA 1 6)" == "luajit" ]; then
-  LUAJIT="yes";
+if [ "${LUA:1:6}" == "luajit" ]; then
+	LUAJIT="yes"
+	LJ_BRANCH="${LUA##luajit}"
 fi
 
-mkdir -p "$LUA_HOME_DIR"
+mkdir -p "${LUA_HOME_DIR}"
 
-if [ "$LUAJIT" == "yes" ]; then
+if [ "${LUAJIT}" == "yes" ]; then
+	if [ "${LUA}" == "luajit" ]; then
+	  curl -LSs "https://github.com/LuaJIT/LuaJIT/archive/v${LUAJIT_VERSION}.tar.gz" | tar xz
+	else
+	  git clone https://github.com/LuaJIT/LuaJIT.git -b "${LJ_BRANCH}" "${LUAJIT_BASE}"
+	fi
 
-  if [ "$LUA" == "luajit" ]; then
-    curl -LSs https://github.com/LuaJIT/LuaJIT/archive/v$LUAJIT_VERSION.tar.gz | tar xz;
-  else
-    git clone https://github.com/LuaJIT/LuaJIT.git $LUAJIT_BASE;
-  fi
+	cd "${LUAJIT_BASE}"
 
-  cd $LUAJIT_BASE
+	if [ "${LUA}" == "luajit2.1" ]; then
+	  # force the INSTALL_TNAME to be luajit
+	  perl -i -pe 's/INSTALL_TNAME=.+/INSTALL_TNAME= luajit/' Makefile
+	fi
 
-  if [ "$LUA" == "luajit2.1" ]; then
-    git checkout v2.1;
-    # force the INSTALL_TNAME to be luajit
-    perl -i -pe 's/INSTALL_TNAME=.+/INSTALL_TNAME= luajit/' Makefile
-  fi
-
-  make && make install PREFIX="$LUA_HOME_DIR"
-
-  ln -s $LUA_HOME_DIR/bin/luajit $HOME/.lua/luajit
-  ln -s $LUA_HOME_DIR/bin/luajit $HOME/.lua/lua;
+	make && make install PREFIX="${LUA_HOME_DIR}"
 
+	ln -s "${LUA_HOME_DIR}/bin/luajit" "${HOME}/.lua/luajit"
+	ln -s "${LUA_HOME_DIR}/bin/luajit" "${HOME}/.lua/lua"
 else
+	if [ "${LUA}" == "lua5.1" ]; then
+	  suff="ftp/lua-5.1.5.tar.gz"
+	elif [ "${LUA}" == "lua5.2" ]; then
+	  suff="ftp/lua-5.2.4.tar.gz"
+	elif [ "${LUA}" == "lua5.3" ]; then
+	  suff="ftp/lua-5.3.5.tar.gz"
+	elif [ "${LUA}" == "lua5.4" ]; then
+	  suff="work/lua-5.4.0-alpha-rc2.tar.gz"
+	fi
 
-  if [ "$LUA" == "lua5.1" ]; then
-    suff="ftp/lua-5.1.5.tar.gz"
-  elif [ "$LUA" == "lua5.2" ]; then
-    suff="ftp/lua-5.2.4.tar.gz"
-  elif [ "$LUA" == "lua5.3" ]; then
-    suff="ftp/lua-5.3.5.tar.gz"
-  elif [ "$LUA" == "lua5.4" ]; then
-    suff="work/lua-5.4.0-alpha-rc2.tar.gz"
-  fi
+	mkdir lua_build -p
+	curl -LSs "http://www.lua.org/${suff}" | tar xz -C lua_build --strip-components=1
+	cd lua_build
 
-  mkdir lua_build
-  curl -LSs http://www.lua.org/"${suff}" | tar xz -C lua_build --strip-components=1
-  cd lua_build
-
-  # Build Lua without backwards compatibility for testing
-  perl -i -pe 's/-DLUA_COMPAT_(ALL|5_[0-9])//' src/Makefile
-  make $PLATFORM
-  make INSTALL_TOP="$LUA_HOME_DIR" install;
-
-  ln -s $LUA_HOME_DIR/bin/lua $HOME/.lua/lua
-  ln -s $LUA_HOME_DIR/bin/luac $HOME/.lua/luac;
+	# Build Lua without backwards compatibility for testing
+	perl -i -pe 's/-DLUA_COMPAT_(ALL|5_[0-9])//' src/Makefile
+	make "${PLATFORM}"
+	make INSTALL_TOP="${LUA_HOME_DIR}" install
 
+	ln -s "${LUA_HOME_DIR}/bin/lua" "${HOME}/.lua/lua"
+	ln -s "${LUA_HOME_DIR}/bin/luac" "${HOME}/.lua/luac"
 fi
 
-cd $TRAVIS_BUILD_DIR
+cd "${TRAVIS_BUILD_DIR}"
 
 lua -v
 
 LUAROCKS_BASE=luarocks-$LUAROCKS
 
-curl -LSs https://luarocks.github.io/luarocks/releases/$LUAROCKS_BASE.tar.gz | tar xz
+curl -LSs https://luarocks.github.io/luarocks/releases/"${LUAROCKS_BASE}".tar.gz | tar xz
 
-cd $LUAROCKS_BASE
+cd "${LUAROCKS_BASE}"
 
-if [ "$LUA" == "luajit" ]; then
-  export LUA_INCDIR="$LUA_HOME_DIR/include/luajit-2.0"
-elif [ "$LUA" == "luajit2.0" ]; then
-  export LUA_INCDIR="$LUA_HOME_DIR/include/luajit-2.0"
-elif [ "$LUA" == "luajit2.1" ]; then
-  export LUA_INCDIR="$LUA_HOME_DIR/include/luajit-2.1"
+if [ "${LUA}" == "luajit" ]; then
+	export LUA_INCDIR="${LUA_HOME_DIR}/include/luajit-2.0"
+elif [ "${LUA}" == "luajit2.0" ]; then
+	export LUA_INCDIR="${LUA_HOME_DIR}/include/luajit-2.0"
+elif [ "${LUA}" == "luajit2.1" ]; then
+	export LUA_INCDIR="${LUA_HOME_DIR}/include/luajit-2.1"
 fi
 
-./configure --with-lua="$LUA_HOME_DIR" --prefix="$LR_HOME_DIR"
+./configure --with-lua="${LUA_HOME_DIR}" --prefix="${LR_HOME_DIR}"
 make build && make install
 
-ln -s $LR_HOME_DIR/bin/luarocks $HOME/.lua/luarocks
+ln -s "${LR_HOME_DIR}/bin/luarocks" "${HOME}/.lua/luarocks"
 
-cd $TRAVIS_BUILD_DIR
+cd "${TRAVIS_BUILD_DIR}"
 
 luarocks --version
 
-rm -rf $LUAROCKS_BASE
+rm -rf "${LUAROCKS_BASE}"
 
-if [ "$LUAJIT" == "yes" ]; then
-  rm -rf $LUAJIT_BASE;
+if [ "${LUAJIT}" == "yes" ]; then
+	rm -rf "${LUAJIT_BASE}"
 else
-  rm -rf lua_build;
+	rm -rf lua_build
 fi