make utility is a build automation tool typically used to read the list of code source files and compilation, linking and building rules in order to create executables and/or libraries. As it's capable of running an arbitrary shell commands and applications, it is possible to use it as a general automation tool.
make reads Makefile in order to find out which files it should operate on and which commands should be run.
Makefile consists of a list of so called targets (or recipies) which come in form:
target: dependency1 dependency2 ...
command1
command2
...
target can be:
- name of the output file which is usually a binary or object file
- name of the arbitrary action e.g. clean, linter etc.
dependency:
- can be:
- names of files which are used as inputs in creating the target file
- names of previously defined targets
- dependencies are optional, they can be omitted in which case the command needs to be in the next line
comand:
- must be written in its own line; if long, it can be break into new line with backslash character
- each command line needs to start with TAB character
- commands are optional in which case the list of dependencies goes in the same line as target label unless backslash is used to break dependencies list into multiple lines
If there are no commands but only dependencies:
target: dependency1 dependency2 ...
If we want to list each dependency in a separate line we can use backslash character to break lines (note that there is a backslash in each line apart the last!)
target: \
dependency1 \
dependency2
If there are no dependencies but only commands:
target:
command1
command2
...
To test the Makefile target syntax, run:
make my_target --dry-run
make commands
ifeq
else
endif
...
They MUST NOT be indented with TAB characters as (almost) all lines with TAB characters as the first character on the line in a makefile are passed to the shell (/bin/sh). The shell doesn't know anything about make commands. make commands can be indented with a set of SPACE characters but this might be misleading as recipies is what MUST be indented with TABs.
Recipies
They must be indented with TAB character in order to be passed to shell.
Targets
Targets are labels that allow make to execute a group of commands together.
Makefile:
target1:
@echo target1 is executing
target2:
@echo target2 is executing
We can now run make as:
$ make target1
or
$ make target2
Minimal (but working) example of Makefile:
docker-run:
@echo Building and running Docker image...
docker build -t cpp-demo . && docker run --rm --name cpp-demo cpp-demo
To run it:
$ make docker-run
Conditional Execution
Use ifeq-endif or ifeq-else-endif blocks.
Makefile:
VAR1= test
VAR2=nottest
demo-if-else-endif:
ifeq($(VAR1), $(VAR2))
...
else
...
endif
Makefile ifeq: when are they evaluated?
Variable comparison
TEST=ON
ifeq ($(TEST),ON)
@echo PASSED
else
@echo FAILED
endif
To check if variable is empty:
ifeq ($(TEST),)
TEST := $(something else)
endif
Makefile set if variable is empty
Using Makefile in Docker projects
Resources:
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