actually use the configure script

.gitignore

@@ -1,2 +1,3 @@
 .DS_store
 build
+configure.mk

Makefile

@@ -1,3 +1,6 @@
+# Load the configure script variables
+-include configure.mk
+
 ##
 ## Directories
 ##

configure

@@ -1,5 +1,53 @@
 #!/bin/sh
 
+set -e
+
+# Show the usage screen
+show_help(){
+  cat <<EOF
+Usage: $0 [OPTION]... [VAR=VALUE]...
+
+To assign environment variables (e.g., FC, FFLAGS...), specify them as
+VAR=VALUE. Defaults for the options are specified in brackets.
+
+Options:
+  -h, --help              display this help and exit
+  --prefix=PREFIX         install files in PREFIX [/usr/local]
+  --enable-static         statically link programs and libraries [no]
+  --disable-static        dynamically link programs and libraries [yes]
+EOF
+}
+
+# Check whether a command exists
+check() {
+  test -z "$1" && return 1
+  printf 'checking for %s... ' "$1"
+  command -v "$1" || (echo 'not found'; exit 1)
+  return $?
+}
+
+# Parse command line options
+for arg in "$@"; do
+  case "$arg" in
+    -h|--help) show_help; exit 0 ;;
+    --prefix=*)
+      PREFIX="${arg#*=}"
+      printf 'install prefix set to %s\n' "$PREFIX"
+      ;;
+    --enable-static) printf 'STATIC=1\n' >> configure.mk ;;
+    --disable-static) ;;
+    *=*)
+      printf '%s\n' "${arg?}" >> configure.mk
+      printf 'set %s\n' "$arg"
+      ;;
+    *) show_help; exit 1 ;;
+  esac
+done
+
+# Truncate the current configuration
+: > configure.mk
+
+# Platform information
 printf 'Running on '
 case $(uname -s) in
   Linux*) echo 'Linux' ;;
@@ -11,24 +59,21 @@ esac
 os=$(uname -r)
 printf 'OS version %s\n' "$os"
 
+# Architecture information
 arch=$(uname -m)
 printf 'Processor architecture %s\n' "$arch"
 
-check() {
-  printf 'Looking for %s... ' "$1"
-  command -v "$1" || (echo 'not found'; exit 1)
-  return $?
-}
+# Variables with a default
+printf '%s=%s\n' PREFIX "${PREFIX:-/usr/local}" >> configure.mk
 
-for FC in ifort gfortran f77; do
-  check $FC && break
+# Detect the Fortran compiler
+for FC in "$FC" ifort gfortran f77; do
+  check "$FC" && break
 done
 # shellcheck disable=SC2181
 if [ $? -ne 0 ]; then
-  printf 'Fortran compiler not found. Cannot proceed\n'
+  printf 'Fortran compiler not found: cannot proceed\n'
   exit 1
-else
-  printf 'Use %s as Fortran compiler\n' "$FC"
 fi
-
-# $FC --version
+printf 'using %s as Fortran compiler\n' "$FC"
+printf '%s=%s\n' FC "$FC" >> configure.mk