# invocation
```sh
# override variables
make CFLAGS='-g -O'
```

## arguments
-   `-B` always make, force compiling of all targets

# variables
-   `CC = gcc` will be expanded when it is used
-   `CC := gcc` will be expanded when it is set
-   `CC ?= gcc` will be set when it doesn't already have a value, may be overwritten by
    any environment
-   `CFLAGS += -ansi` append

# automatic variables
-   `$@` file name of target
-   `$*` stem of matching, target: `dir/a.foo.b`, pattern: `a.%.b`, stem: `dir/foo`
-   `$<` name of first prerequisite
-   `$?` names of all the prerequisites that are newer than the target
-   `$^` names of all the prerequisites, with spaces between them
-   `$+` names of all the prerequisites, with spaces between them, with duplicates
-   following two work with `<`, `?`, ... in place of `@` as well:
-   `$(@F)` dir part of the file name of the target, without trailing slash
-   `$(@D)` file-within-directory part of the file name of the target

# functions
```make
sources   := $(wildcard *.src)
targets   := $(sources:.src=.trg)
filtered  := $(filter-out broken.src, $(sources))
term_cols := $(shell tput cols)
```

# special targets
-   `.DELETE_ON_ERROR`
-   `.NOTPARALLEL` affects all targets in file
-   `.PHONY`
-   `.IGNORE` old way to ignore errors in recipe

# commands
-   `-` before command ignores its errors
-   `@` don't display command

# pattern

## loops
```make
subdirs := $(wildcard */)

.PHONY: all
all: $(subdirs)

.PHONY: $(subdirs)
$(subdirs):
    $(MAKE) -C $@
```

# conventions
## variables
uppercase letters are traditional, however gnu recommends lowercase for internal
purposes and uppercase for variables that control implicit rules or parameters
intended to be overwritten by caller.

## gnu standard targets
-   `all`
-   `dist` create distribution tar file
-   `check` run tests which require build but no installation
-   `installcheck` perform tests after `install`, don't assume `$(bindir)` is in path
-   `install`
-   `install-strip` strip removes information such as debugging symbols
-   `uninstall`
-   `clean` don't delete config files
-   `distclean` like a fresh checkout
-   `mostlyclean` like `clean`, but leave costly files
-   `maintainer-clean` distclean plus more: may need other tools to rebuild, not intended for normal users
-   `html`, `pdf`, `install-html`, `install-pdf` doc in other format than `info`