makefile - Make dummy target that checks the age of an existing file? -


i'm using make control data flow in statistical analysis. if have raw data in directory ./data/raw_data_files, , i've got data manipulation script creates cleaned data cache @ ./cache/clean_data. make rule like:

cache/clean_data:   scripts/clean_data

i not want touch data in ./data/, either make, or of data munging scripts. there way in make create dependency cache/clean_data checks whether specific files in ./data/ newer last time make ran?

if clean_data single file, let depend on data files:

cache/clean_data: data/*     scripts/clean_data

if directory containing multiple cleaned files, easiest way write stamp file , have depend on data files:

cache/clean_data-stamp: data/*     scripts/clean_data     touch cache/clean_data-stamp

note regenerates clean_data files if 1 data file changes. more elaborate approach possible if have 1-to-1 mapping between data , cleaned files. gnu make manual has decent example of this. here adaptation:

 datafiles:= $(wildcard data/*)  cachefiles:= $(patsubst data/%,cache/clean_data/%,$(datafiles))   cache/clean_data/% : data/%          scripts/clean_data --input $< --output $@   all: $(cachefiles)

here, use wildcard list of files under data. replace data path cache path using patsubst. tell make how generate cache files via static pattern rule, , finally, define target all generates required cache files.

of course can list cachefiles explicitly in makefile (cachefiles:= cache/clean_data/a cache/clean_data/b), typically more convenient let make handle automatically, if possible.

notice complex example works gnu make, not in windows' nmake. further info, consult gnu make manual, great resource makefile needs.


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