On Sun, 18 Jun 2017 13:03:10 +0200
SF Markus Elfring <elfr...@users.sourceforge.net> wrote:
> I have tried the following small script out together with the program
> âGNU Make 4.2.1-1.7â on my openSUSE Tumbleweed system.
That "script" seems like a makefile to me.
> my_compilation?=echo
> my_preparation?=cat
> footer?=MOTD.txt
> prepared_file?=MOTD.in
>
> MOTD%.log: MOTD%.txt MOTD%.in
> ${my_compilation} "$<: $$(cat ${prepared_file} ${footer})" > $@
>
> ${prepared_file}: MOTD.draft
> ${my_preparation} $< > $@
>
>
> elfring@Sonne:~/Projekte/Bau> my_message=MOTD.log && rm -f
> ${my_message}; touch MOTD.draft MOTD.txt && LANG=C make
> --no-builtin-rules -f ../rule-check2.make && LANG=C ls -l MOTD.in
> ${my_message} cat MOTD.draft > MOTD.in
> ls: cannot access 'MOTD.log': No such file or directory
> -rw-r--r-- 1 elfring users 6 Jun 18 12:56 MOTD.in
>
>
> Now I wonder why the log file is not generated by this build approach at
> the end. Where is my knowledge and understanding incomplete for this
> software situation?
Your MOTD.log is not generated because you did not tell make to generate
it. It would have been generated if you would have called make with a
command like:
LANG=C make --no-builtin-rules -f ../rule-check2.make MOTD.log
and if you had a rule to build MOTD.log
It would also have been generated if your makefile would have contained a
default rule which caused that file to be generated.
The default rule in your makefile is ${prepared_file} which in this case
is MOTD.in gets generated.
There is no default rule for MOTD.txt, your makefile know how to generate
every MOTD?*.txt but it does not know if any of them should be generated
by default. In the documentation at
https://www.gnu.org/software/make/manual/html_node/Rules.html it says:
"a target that defines a pattern rule has no effect on the default goal."
In fact, there is no rule at all for MOTD.txt as your rule for MOTD%.txt
has a pattern which must match a none empty string.
regards Henrik
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