Question

I’m trying to create a Makefile that will download and process file a file to generate targets, this is a simplified version:

default: all
.PHONY: all clean filelist.d
clean:
    @rm -fv *.date *.d

#The actual list comes from a FTP file, but let's simplify things a bit
filelist.d:
    @echo "Getting updated filelist..."
    @echo "LIST=$(shell date +\%M)1.date $(shell date +\%M)2.date" > $@
    @echo 'all: $$(LIST)' >> $@

%.date:
    touch $@

-include filelist.d

Unfortunately the target all doesn’t get updated properly on the first run, it needs to be run again to get the files. This is the output I get from it:

 $ make
Getting updated filelist...
make: Nothing to be done for `default'.
 $ make
Getting updated filelist...
touch 141.date
touch 142.date
touch 143.date

I’m using GNU Make 3.81 whose documentation states that it reloads the whole thing if the included files get changed. What is going wrong?

Answer 1

You have specified filelist.d as a .PHONY target, so make believes making that target doesn’t actually update the specified file. However, it does, and the new contents are used on the next run. For the first run, the missing file isn’t an error because include is prefixed with the dash.

Remove filelist.d from .PHONY. However, remember it won’t be regenerated again until you delete it (as it doesn’t depend on anything).

By the same token, you should include “default” in .PHONY.

---

I wrote a shell script rather than lump all this in the makefile:

#!/bin/bash
# Check whether file $1 is less than $2 days old.

[ $# -eq 2 ] || {
  echo "Usage: $0 FILE DAYS" >&2
  exit 2
}

FILE="$1"
DAYS="$2"

[ -f "$FILE" ] || exit 1  # doesn't exist or not a file

TODAY=$(date +%s)
TARGET=$(($TODAY - ($DAYS * 24 * 60 * 60)))
MODIFIED=$(date -r "$FILE" +%s)

(($TARGET < $MODIFIED))

Replace X with the max number of days that can pass before filelist.d is downloaded again:

filelist.d: force-make
        ./less-than-days $@ X || command-to-update
.PHONY: force-make
force-make:

Now filelist.d depends on a .PHONY target, without being a phony itself. This means filelist.d is always out of date (phony targets are always “new”), but its recipe only updates the file periodically.

Unfortunately, this requires you to write the update command as a single command, and space may be a problem if it is long. In that case, I would put it in a separate script as well.