CODEWITHSUNDEEP
makefile
Ninja2k
Ninja2k

Reputation: 879

Makefile FILES command will not execute

I am trying to learn Make syntax, I have instructed it to compile a file and it does this correctly, when I tell it to execute a shell command to create a file using touch it does not do this, it returns no error to indicate anything is wrong.

Commands

HelloWorld: HelloWorld.c
    gcc -o HelloWorld HelloWorld.c 

FILES="$(shell touch > file1.txt)"

Upvotes: 0

Views: 3023

Answers (2)

HardcoreHenry
HardcoreHenry

Reputation: 6387

I think you want:

 $(shell touch file1.txt)

(Notice the lack of a > redirect in there). Also touch does not output anything to stdout, therefore FILES would be blank no matter what, so the assignment is useless.

If you're going to do things like this be aware that the $(shell ...) commands (in the global scope) are executed at parse time, before any of the recipes are run.

------------ EDIT -------------

In regards to your question about creating a blank file:

all:
$(info output $(shell echo "hello world"))
$(shell touch file1.txt)

should produce your file:

> ls file1.txt; make; ls file1.txt
file1.txt
output hello world
make-3.81: Nothing to be done for `all'.
file1.txt

Upvotes: 1

MadScientist
MadScientist

Reputation: 101051

As pointed out already your syntax is wrong. But beyond that your shell function is never even executed.

Why not? Because in your makefile, you define a variable which contains the shell variable invocation but then you never use the variable anywhere. Since you don't use it, the variable is never expanded. Since the variable is never expanded, the function in it is never invoked.

If you want the variable to be expanded you either need to make it a simple variable (using :=) so that the right-hand side is expanded when the variable is assigned, or you have to use the function in a context where it's expanded immediately; the other answer has an example of using that (outside of any variable assignment)

Here's an example of using a simple variable:

HelloWorld: HelloWorld.c
        gcc -o HelloWorld HelloWorld.c 

FILES := $(shell touch file1.txt)

(note you don't need quotes when setting makefile variables, unlike shell variables).

As for the manual, it's written to be a user guide: that is you're supposed to read it starting at the beginning, rather than a reference manual where you jump around. In particular you won't get anywhere writing makefiles until you read carefully and fully understand the initial two chapter "Introduction to Makefiles" and "Writing Makefiles". For fluency you need to understand the section How make Reads a Makefile.

Upvotes: 2

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