use variable instead of file

buildscript.sh

 #!/bin/bash
+set -e
 echo ${MAXIMA_VERSION?Error \$MAXIMA_VERSION is not defined} \
      ${SBCL_VERSION?Error \$SBCL_VERSION is not defined}
   
@@ -12,15 +13,15 @@ apt-get install -y bzip2 make wget python3 gcc texinfo
 
 mkdir -p ${SRC}
 wget https://sourceforge.net/projects/maxima/files/Maxima-source/${MAXIMA_VERSION}-source/maxima-${MAXIMA_VERSION}.tar.gz -O ${SRC}/maxima-${MAXIMA_VERSION}.tar.gz
-wget https://sourceforge.net/projects/sbcl/files/sbcl/${SBCL_VERSION}/sbcl-${SBCL_VERSION}-$(cat /SBCL_ARCH)-linux-binary.tar.bz2 -O ${SRC}/sbcl-${SBCL_VERSION}-$(cat /SBCL_ARCH)-linux.tar.bz2
+wget https://sourceforge.net/projects/sbcl/files/sbcl/${SBCL_VERSION}/sbcl-${SBCL_VERSION}-${SBCL_ARCH}-linux-binary.tar.bz2 -O ${SRC}/sbcl-${SBCL_VERSION}-${SBCL_ARCH}-linux.tar.bz2
 
 # Compile sbcl
 cd ${SRC}
-bzip2 -d sbcl-${SBCL_VERSION}-$(cat /SBCL_ARCH)-linux.tar.bz2
-tar -xf sbcl-${SBCL_VERSION}-$(cat /SBCL_ARCH)-linux.tar
-rm sbcl-${SBCL_VERSION}-$(cat /SBCL_ARCH)-linux.tar
+bzip2 -d sbcl-${SBCL_VERSION}-${SBCL_ARCH}-linux.tar.bz2
+tar -xf sbcl-${SBCL_VERSION}-${SBCL_ARCH}-linux.tar
+rm sbcl-${SBCL_VERSION}-${SBCL_ARCH}-linux.tar
 ls
-cd sbcl-${SBCL_VERSION}-$(cat /SBCL_ARCH)-linux
+cd sbcl-${SBCL_VERSION}-${SBCL_ARCH}-linux
 ./install.sh
 
 # Compile maxima