wrote usage function and set sensible defaults

cbuild.sh

@@ -6,10 +6,10 @@
 
 # --- USER CONFIG ---
 CC="gcc"
-CFLAGS="-Wall -Wpedantic -std=c99"
+CFLAGS="-Wall -Wpedantic"
 LDFLAGS=""
 LDLIBS=""
-TARGET="foo"
+TARGET="a.out"
 SRCDIR="src"
 OBJDIR="obj"
 MAKEFILE=".makefile"
@@ -24,6 +24,41 @@ OBJ="$(find ${SRCDIR} -name '*\.c' |
 
 srcnum="$(find ${SRCDIR} -name '*\.c' -exec printf %c {} + | wc -c)"
 
+usage() {
+    cat <<EOF
+cbuild.sh: A simple, customizable, automated, and portable build script for C
+projects. This script works by automatically detecting .c source files in
+SRCDIR, generating a makefile, compiling them into objects in OBJDIR, and
+finally linking them to TARGET.
+
+Customization:
+    Open cbuild.sh in your editor and navigate to the USER CONFIG section (at
+    the top of the file).
+
+    CC        the compiler to use   (default: gcc)
+    CFLAGS    compilation flags     (default: -Wall -Wpedantic)
+    LDFLAGS   linker flags          (default: none)
+    LDLIBS    linker libraries      (default: none)
+    TARGET    final target to link  (default: a.out)
+    SRCDIR    the directory where the script will search for .c source files
+              (default: src)
+    OBJDIR    the directory where compiled objects will be placed. (default: obj)
+    MAKEFILE  the filename of the generated makefile (default: .makefile)
+
+Usage:
+    ./cbuild.sh [COMMAND]
+    
+    COMMAND:
+    build     generate the makefile, compile objects and link target.
+    clean     remove makefile, objects, and target.
+    buildcn   clean, and then build.
+    generate  ONLY generate the makefile.
+    run       build, then execute TARGET.
+    dryrun    print all commands that will be executed during the build process
+              to stdout.
+EOF
+}
+
 export_vars() {
     export CC
     export CFLAGS
@@ -121,6 +156,7 @@ __progress__() {
 
     echo "${2}"
 }
+
 case $1 in
     build) build;;
     clean) clean;;
@@ -129,4 +165,5 @@ case $1 in
     run) run;;
     dryrun) dry_run;;
     __progress__) __progress__ "${2}" "${3}";;
+    *) usage;;
 esac