Merge pull request #168 from swcarpentry/auto-vars

Automatic variables

_episodes/04-dependencies.md

@@ -217,16 +217,16 @@ downstream steps.
 {: .challenge}
 
 We still have to add the `testzipf.py` script as dependency to
-`results.txt`. Given the answer to the challenge above, we cannot use
-`$^` in the rule.
-We can however move `testzipf.py` to be the
-first dependency and then use `$<` to refer to it.
-In order to refer to the `.dat` files, we can just use `*.dat` for now (we will
-cover a better solution later on).
+`results.txt`.
+Given the answer to the challenge above,
+we need to make a couple of small changes so that we can still use automatic variables.
+
+We'll move `testzipf.py` to be the first dependency and then edit the action
+so that we pass all the dependencies as arguments to python using `$^`.
 
 ~~~
 results.txt : testzipf.py isles.dat abyss.dat last.dat
-	python $< *.dat > $@
+	python $^ > $@
 ~~~
 {: .language-make}
 

_episodes/05-patterns.md

@@ -18,19 +18,18 @@ rule]({{ page.root }}/reference.html#pattern-rule) which can be used to build an
 `.dat` file from a `.txt` file in `books/`:
 
 ~~~
-%.dat : books/%.txt countwords.py
-	python countwords.py $< $*.dat
+%.dat : countwords.py books/%.txt
+	python $^ $@
 ~~~
 {: .language-make}
 
-`%` is a Make [wildcard]({{ page.root }}/reference.html#wildcard).  `$*` is a special
-variable which gets replaced by the [stem]({{ page.root }}/reference.html#stem) with
-which the rule matched.
+`%` is a Make [wildcard]({{ page.root }}/reference.html#wildcard),
+matching any number of any characters.
 
 This rule can be interpreted as:
 "In order to build a file named `[something].dat` (the target)
-find a file named `books/[that same something].txt` (the dependency)
-and run `countwords.py [the dependency] [the target]`."
+find a file named `books/[that same something].txt` (one of the dependencies)
+and run `python [the dependencies] [the target]`."
 
 If we re-run Make,
 
@@ -77,14 +76,14 @@ Our Makefile is now much shorter and cleaner:
 ~~~
 # Generate summary table.
 results.txt : testzipf.py isles.dat abyss.dat last.dat
-	python $< *.dat > $@
+	python $^ > $@
 
 # Count words.
 .PHONY : dats
 dats : isles.dat abyss.dat last.dat
 
-%.dat : books/%.txt countwords.py
-	python countwords.py $< $*.dat
+%.dat : countwords.py books/%.txt
+	python $^ $@
 
 .PHONY : clean
 clean :
@@ -99,15 +98,3 @@ clean :
 > contains all of our work so far.
 {: .callout}
 
-This episode has introduced pattern rules, and used the `$*` variable
-in the `dat` rule in order to explain how to use it.
-Arguably, a neater solution would have been to use `$@` to refer to
-the target of the current rule (see below),
-but then we wouldn't have learned about `$*`.
-
-```
-%.dat : books/%.txt countwords.py
-	python countwords.py $< $@
-```
-{: .language-make}
-

_episodes/06-variables.md

@@ -29,13 +29,10 @@ COUNT_SRC=countwords.py
 This is a variable [assignment]({{ page.root }}/reference.html#assignment) -
 `COUNT_SRC` is assigned the value `countwords.py`.
 
-`countwords.py` is our script and it is invoked by passing it to
-`python`. We can introduce another couple of variables to represent this
-execution:
+We can do the same thing with the interpreter language used to run the script:
 
 ~~~
 LANGUAGE=python
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 ~~~
 {: .language-make}
 
@@ -46,11 +43,9 @@ write it, or reference it, in this way.
 
 Here we reference the variables `LANGUAGE` and `COUNT_SRC`. This tells Make to
 replace the variable `LANGUAGE` with its value `python`,
-and to replace the variable `COUNT_SRC` with its value `countwords.py`. When
-Make is run it will assign to `COUNT_EXE` the value `python
-countwords.py`.
+and to replace the variable `COUNT_SRC` with its value `countwords.py`.
 
-Defining the variable `COUNT_EXE` in this way avoids repeating `python` in our 
+Defining the variable `LANGUAGE` in this way avoids repeating `python` in our
 Makefile, and allows us to easily
 change how our script is run (e.g. we might want to use a different
 version of Python and need to change `python` to `python2` -- or we might want
@@ -59,10 +54,10 @@ to rewrite the script using another language (e.g. switch from Python to R)).
 > ## Use Variables
 >
 > Update `Makefile` so that the `%.dat` rule
-> references the variables `COUNT_SRC` and `COUNT_EXE`.
+> references the variable `COUNT_SRC`.
 > Then do the same for the `testzipf.py` script
 > and the `results.txt` rule,
-> using `ZIPF_SRC` and `ZIPF_EXE` as variable names
+> using `ZIPF_SRC` as the variable name.
 >
 > > ## Solution
 > > [This Makefile]({{ page.root }}/code/06-variables-challenge/Makefile)
@@ -79,11 +74,9 @@ the original Makefile). Let us create `config.mk`:
 # Count words script.
 LANGUAGE=python
 COUNT_SRC=countwords.py
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 
 # Test Zipf's rule
 ZIPF_SRC=testzipf.py
-ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)
 ~~~
 {: .language-make}
 
@@ -103,7 +96,7 @@ $ make results.txt
 ~~~
 {: .language-bash}
 
-We have separated the configuration of our Makefile from its rules,
+We have separated the configuration of our Makefile from its rules --
 the parts that do all the work. If we want to change our script name
 or how it is executed we just need to edit our configuration file, not
 our source code in `Makefile`. Decoupling code from configuration in

_episodes/07-functions.md

@@ -19,14 +19,14 @@ include config.mk
 
 # Generate summary table.
 results.txt : $(ZIPF_SRC) isles.dat abyss.dat last.dat
-	$(ZIPF_EXE) *.dat > $@
+	$(LANGUAGE) $^ > $@
 
 # Count words.
 .PHONY : dats
 dats : isles.dat abyss.dat last.dat
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $*.dat
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^ $@
 
 .PHONY : clean
 clean :
@@ -132,14 +132,6 @@ clean :
 ~~~
 {: .language-make}
 
-Let's also tidy up the `%.dat` rule by using the automatic variable `$@` instead
-of `$*.dat`:
-
-```
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $@
-```
-{: .language-make}
 
 Let's check:
 
@@ -163,7 +155,7 @@ We can also rewrite `results.txt`:
 
 ~~~
 results.txt : $(ZIPF_SRC) $(DAT_FILES)
-	$(ZIPF_EXE) $(DAT_FILES) > $@
+	$(LANGUAGE) $^ > $@
 ~~~
 {: .language-make}
 
@@ -215,14 +207,14 @@ DAT_FILES=$(patsubst books/%.txt, %.dat, $(TXT_FILES))
 
 # Generate summary table.
 results.txt : $(ZIPF_SRC) $(DAT_FILES)
-	$(ZIPF_EXE) $(DAT_FILES) > $@
+	$(LANGUAGE) S^ > $@
 
 # Count words.
 .PHONY : dats
 dats : $(DAT_FILES)
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $@
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^ $@
 
 .PHONY : clean
 clean :
@@ -242,11 +234,9 @@ Remember, the `config.mk` file contains:
 # Count words script.
 LANGUAGE=python
 COUNT_SRC=countwords.py
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 
 # Test Zipf's rule
 ZIPF_SRC=testzipf.py
-ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)
 ~~~
 {: .language-make}
 

_episodes/08-self-doc.md

@@ -59,14 +59,14 @@ which `sed` can detect. Since Make uses `#` for comments, we can use
 ~~~
 ## results.txt : Generate Zipf summary table.
 results.txt : $(ZIPF_SRC) $(DAT_FILES)
-	$(ZIPF_EXE) $(DAT_FILES) > $@
+	$(LANGUAGE) $^ > $@
 
 ## dats        : Count words in text files.
 .PHONY : dats
 dats : $(DAT_FILES)
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $@
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^ $@
 
 ## clean       : Remove auto-generated files.
 .PHONY : clean

code/04-dependencies/Makefile

@@ -1,6 +1,6 @@
 # Generate summary table.
 results.txt : testzipf.py isles.dat abyss.dat last.dat
-	python $< *.dat > $@
+	python $^ > $@
 
 # Count words.
 .PHONY : dats

code/05-patterns/Makefile

@@ -1,13 +1,13 @@
 # Generate summary table.
 results.txt : testzipf.py isles.dat abyss.dat last.dat
-	python $< *.dat > $@
+	python $^ > $@
 
 # Count words.
 .PHONY : dats
 dats : isles.dat abyss.dat last.dat
 
-%.dat : books/%.txt countwords.py
-	python countwords.py $< $*.dat
+%.dat : countwords.py books/%.txt
+	python $^ $@
 
 .PHONY : clean
 clean :

code/06-variables-challenge/Makefile

@@ -1,19 +1,17 @@
 LANGUAGE=python
 COUNT_SRC=countwords.py
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 ZIPF_SRC=testzipf.py
-ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)
 
 # Generate summary table.
 results.txt : $(ZIPF_SRC) isles.dat abyss.dat last.dat
-	$(ZIPF_EXE) *.dat > $@
+	$(LANGUAGE) $^ > $@
 
 # Count words.
 .PHONY : dats
 dats : isles.dat abyss.dat last.dat
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $*.dat
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^ $@
 
 .PHONY : clean
 clean :

code/06-variables/Makefile

@@ -2,14 +2,14 @@ include config.mk
 
 # Generate summary table.
 results.txt : $(ZIPF_SRC) isles.dat abyss.dat last.dat
-	$(ZIPF_EXE) *.dat > $@
+	$(LANGUAGE) $^ > $@
 
 # Count words.
 .PHONY : dats
 dats : isles.dat abyss.dat last.dat
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $*.dat
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^
 
 .PHONY : clean
 clean :

code/06-variables/config.mk

@@ -1,8 +1,6 @@
 # Count words script.
 LANGUAGE=python
 COUNT_SRC=countwords.py
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 
 # Test Zipf's rule
 ZIPF_SRC=testzipf.py
-ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)

code/07-functions/Makefile

@@ -5,14 +5,14 @@ DAT_FILES=$(patsubst books/%.txt, %.dat, $(TXT_FILES))
 
 # Generate summary table.
 results.txt : $(ZIPF_SRC) $(DAT_FILES)
-	$(ZIPF_EXE) $(DAT_FILES) > $@
+	$(LANGUAGE) $^ > $@
 
 # Count words.
 .PHONY : dats
 dats : $(DAT_FILES)
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $@
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^ $@
 
 .PHONY : clean
 clean :

code/07-functions/config.mk

@@ -1,8 +1,6 @@
 # Count words script.
 LANGUAGE=python
 COUNT_SRC=countwords.py
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 
 # Test Zipf's rule
 ZIPF_SRC=testzipf.py
-ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)

code/09-conclusion-challenge-1/Makefile

@@ -10,21 +10,21 @@ all : results.txt $(PNG_FILES)
 
 ## results.txt : Generate Zipf summary table.
 results.txt : $(ZIPF_SRC) $(DAT_FILES)
-	$(ZIPF_EXE) $(DAT_FILES) > $@
+	$(LANGUAGE) $^ > $@
 
 ## dats        : Count words in text files.
 .PHONY : dats
 dats : $(DAT_FILES)
 
-%.dat : books/%.txt $(COUNT_SRC)
-	$(COUNT_EXE) $< $@
+%.dat : $(COUNT_SRC) books/%.txt
+	$(LANGUAGE) $^ $@
 
 ## pngs        : Plot word counts.
 .PHONY : pngs
 pngs : $(PNG_FILES)
 
-%.png : %.dat $(PLOT_SRC)
-	$(PLOT_EXE) $< $@
+%.png : $(PLOT_SRC) %.dat
+	$(LANGUAGE) $^ $@
 
 ## clean       : Remove auto-generated files.
 .PHONY : clean

code/09-conclusion-challenge-1/config.mk

@@ -1,12 +1,9 @@
 # Count words script.
 LANGUAGE=python
 COUNT_SRC=countwords.py
-COUNT_EXE=$(LANGUAGE) $(COUNT_SRC)
 
 # Plot word counts script.
 PLOT_SRC=plotcounts.py
-PLOT_EXE=$(LANGUAGE) $(PLOT_SRC)
 
 # Test Zipf's rule
 ZIPF_SRC=testzipf.py
-ZIPF_EXE=$(LANGUAGE) $(ZIPF_SRC)