Create a variable in a makefile by reading content

Question

How can I create a variable on-the-fly from makefile, the value of which would be the entire contents of another data file.

Answer 1

Much simpler since $(file op filename) was added:

VARIABLE = $(file < my_file.txt)

Manual page here: https://www.gnu.org/software/make/manual/html_node/File-Function.html#index-file_002c-reading-from

Answer 2

As the platform has not been specified, this is the way how it works on Solaris:

VERSION:sh = cat VERSION

all:
        echo $(VERSION)

Answer 3

cat doesn't exist on Windows. Solution that works for Linux and Windows:

cat := $(if $(filter $(OS),Windows_NT),type,cat)
variable := $(shell $(cat) filename)

Explanation: Seems like On Windows there is always OS environment variable defined to be equal to 'Windows_NT'. This way, for Windows type command is used, for non-Windows cat is used.

Answer 4

GNU make version 4.2 supports file reading operation, so with respect to Maxim Egorushkin's great answer there is an optional way to solve this problem now:

FILE     := test.txt
variable :=$(file < $(FILE))

Answer 5

If you are using GNU make, another way to get this effect is to use a make "include" of another makefile:

From Makefile:

include "./MyFile.mak"

Create a file "MyFile.mak" with content:

FILE := "my file content"
FILE += "more content 1"
FILE += "more content 2"

Answer 6

Assuming GNU make:

file := whatever.txt
variable := $(shell cat ${file})