Conditional Dependencies in Make

Make is the de facto build tool on Linux. I needed a way to conditionally require a dependency. Here is how I did it:

Before any of the executable code, I placed this if clause:

ifeq ($(findstring $(TARGET),$(wildcard *.s)), $(TARGET))
    conditional_file_exists = $(TARGET).o
    conditional_file_exists = $()

Then, I placed $(conditional_file_exists) in the dependency list. If that .s file exists, it adds the object file to the dependency list, otherwise it doesn’t.

$(AXF_FILE): $(C_FILE).o $(conditional_file_exists)

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