build: allow minimal installation with Makefile

the `minimal` target allows a minimal installation without the man pages
or the shell completion files

Makefile

@@ -1,40 +1,84 @@
-PROG ?= tessen
-PREFIX ?= /usr
+# `?=` assigns value to a variable only if it has not been set before
+# this can be useful when you want to override variables during execution of
+# the make command
+# for example, sudo make PREFIX=/custom/dir install
 DESTDIR ?=
-BINDIR ?= $(PREFIX)/bin
-MANDIR ?= $(PREFIX)/share/man
-BASHCOMPDIR ?= $(PREFIX)/share/bash-completion/completions
-FISHCOMPDIR ?= $(PREFIX)/share/fish/vendor_completions.d
+PREFIX ?= /usr
+BINDIR ?= ${PREFIX}/bin
+DATAROOTDIR ?= ${PREFIX}/share
+MANDIR ?= ${DATAROOTDIR}/man
+BASHCOMPDIR ?= ${DATAROOTDIR}/bash-completion/completions
+FISHCOMPDIR ?= ${DATAROOTDIR}/fish/vendor_completions.d
+PROG ?= tessen
 
+# `:=` is simple variable assignment and variables which are part of the values
+# being assigned are expanded only if they are already set
 RM := rm
+# `@echo` prevents the command itself from being printed
 ECHO := @echo
 SCDOC := scdoc
 INSTALL := install
 
-.PHONY: all man install clean uninstall
+# this is where the basic structure of Makefiles start and it looks like
+# file_a : file_b
+# 	command
+# 	command
+# 	...
+#
+# file_b: file_c
+# 	command
+# 	command
+# 	...
+#
+# file_a needs file_b and file_b needs file_c - this is how Makefiles operate
+
+# file_a can be a `.PHONY`, a special target, which says that the files `all`,
+# `man` etc aren't really files but other targets
+# think of them as pseudo files or fake files which don't exist but serve to
+# execute commands in a certain logical sequence
+# by default, if nothing is specified, the `all` target is executed
+.PHONY: all install minimal bashcomp fishcomp clean uninstall
 
 all:
-	$(ECHO) "$(PROG) is a shell script and doesn't need to be compiled"
-	$(ECHO) "To install it, enter \"make install\""
+	${ECHO} "${PROG} is a shell script and doesn't need to be compiled"
+	${ECHO} "To install it, enter \"make install\""
+
+install: man bashcomp fishcomp
+	${INSTALL} -Dm 0755 ${PROG} -t ${DESTDIR}${BINDIR}
+	${ECHO} ""
+	${ECHO} "${PROG} has been installed succesfully"
 
-man: man/tessen.1
+# a minimal alternative for people who don't want completion files or man pages
+# `make man`, `make install_man`, `make bashcomp`, `man fishcomp`, and `make
+# minimal` can be used selectively to install what's needed
+minimal:
+	${INSTALL} -Dm 0755 ${PROG} -t ${DESTDIR}${BINDIR}
+	${ECHO} ""
+	${ECHO} "${PROG} has been installed succesfully"
 
+man: man/${PROG}.1 man/${PROG}.5
+	${INSTALL} -Dm 0644 man/${PROG}.1 -t ${DESTDIR}${MANDIR}/man1
+	${INSTALL} -Dm 0644 man/${PROG}.5 -t ${DESTDIR}${MANDIR}/man5
+
+# we want *.scd files from the files that are inside man/
+# the `$^` is an automatic variable which means the list of `file_b`'s
+# the `$@` is an automatic variable which means the list of `file_a`'s
 man/%: man/%.scd
-	$(SCDOC) < $^ > $@
+	${SCDOC} < $^ > $@
+
+bashcomp:
+	${INSTALL} -Dm 0644 completion/${PROG}.bash-completion ${DESTDIR}${BASHCOMPDIR}/${PROG}
 
-install: man
-	$(INSTALL) -Dm 0755 $(PROG) -t $(DESTDIR)$(BINDIR)
-	$(INSTALL) -Dm 0644 man/*.1 -t $(DESTDIR)$(MANDIR)/man1
-	$(INSTALL) -Dm 0644 completion/$(PROG).bash-completion $(DESTDIR)$(BASHCOMPDIR)/$(PROG)
-	$(INSTALL) -Dm 0644 completion/$(PROG).fish-completion $(DESTDIR)$(FISHCOMPDIR)/$(PROG).fish
-	$(ECHO) ""
-	$(ECHO) "$(PROG) has been installed succesfully"
+fishcomp:
+	${INSTALL} -Dm 0644 completion/${PROG}.fish-completion ${DESTDIR}${FISHCOMPDIR}/${PROG}.fish
 
 clean:
-	$(RM) -f man/*.1
+	${RM} -f man/${PROG}.1
+	${RM} -f man/${PROG}.5
 
 uninstall:
-	$(RM) -f "$(DESTDIR)$(BINDIR)/$(PROG)"
-	$(RM) -f "$(DESTDIR)$(MANDIR)/man1/$(PROG).1"
-	$(RM) -f "$(DESTDIR)$(BASHCOMPDIR)/$(PROG)"
-	$(RM) -f "$(DESTDIR)$(FISHCOMPDIR)/$(PROG).fish"
+	${RM} -f "${DESTDIR}${BINDIR}/${PROG}"
+	${RM} -f "${DESTDIR}${MANDIR}/man1/${PROG}.1"
+	${RM} -f "${DESTDIR}${MANDIR}/man5/${PROG}.5"
+	${RM} -f "${DESTDIR}${BASHCOMPDIR}/${PROG}"
+	${RM} -f "${DESTDIR}${FISHCOMPDIR}/${PROG}.fish"