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authorJohannes Stoelp <johannes.stoelp@gmail.com>2024-03-27 00:14:40 +0100
committerJohannes Stoelp <johannes.stoelp@gmail.com>2024-03-27 00:14:40 +0100
commit0ccba0943d477b71cdccd2505eb81b95f091263a (patch)
tree50b5518c849a0792489ab873a2fa2878ce4891a1 /src
parent1ea7da67c3186119551ff88c5c6b05de05393ce0 (diff)
downloadnotes-0ccba0943d477b71cdccd2505eb81b95f091263a.tar.gz
notes-0ccba0943d477b71cdccd2505eb81b95f091263a.zip
make: add call,eval,foreach & multi-line var
Diffstat (limited to 'src')
-rw-r--r--src/development/make.md96
1 files changed, 95 insertions, 1 deletions
diff --git a/src/development/make.md b/src/development/make.md
index fdef47e..38da4fa 100644
--- a/src/development/make.md
+++ b/src/development/make.md
@@ -13,7 +13,7 @@ target .. : prerequisite ..
> Use `make -p` to print all rules and variables (implicitly + explicitly defined).
-## Pattern rules & Automatic variables
+## Pattern rules & variables
### Pattern rules
A pattern rule contains the `%` char (exactly one of them) and look like this example:
```make
@@ -72,6 +72,22 @@ Running above `Makefile` gives:
Variables related to filesystem paths:
- `$(CURDIR)`: Path of current working dir after using `make -C path`
+### Multi-line variables
+```make
+define my_var
+@echo foo
+@echo bar
+endef
+
+all:
+ $(my_var)
+```
+Running above `Makefile` gives:
+```text
+foo
+bar
+```
+
## Arguments
Arguments specified on the command line *override* ordinary variable
@@ -130,6 +146,7 @@ out := $(filter-out %.b %.c, $(in))
Resolve each file name as absolute path (don't resolve symlinks).
```make
$(abspath fname1 fname2 ..)
+```
### `realpath`
Resolve each file name as canonical path.
@@ -137,6 +154,53 @@ Resolve each file name as canonical path.
$(realpath fname1 fname2 ..)
```
+### `call` ([ref][make-call])
+Invoke parametrized function, which is an expression saved in a variable.
+```make
+swap = $(2) $(1)
+
+all:
+ @echo "call swap first second -> $(call swap,first,second)"
+```
+Outputs:
+```text
+call swap first second -> second first
+```
+
+### `eval` ([ref][make-eval])
+Allows to define new makefile constructs by evaluating the result of a variable
+or function.
+```make
+define new_rule
+$(1):
+ @echo "$(1) -> $(2)"
+endef
+
+default: rule1 rule2
+
+$(eval $(call new_rule,rule1,foo))
+$(eval $(call new_rule,rule2,bar))
+```
+Outputs:
+```text
+rule1 -> foo
+rule2 -> bar
+```
+
+### foreach ([ref][make-foreach])
+Repeat a piece of text for a list of values, given the syntax `$(foreach
+var,list,text)`.
+```make
+myfn = x$(1)x
+
+default:
+ @echo $(foreach V,foo bar baz,$(call myfn,$(V)))
+```
+Outputs:
+```text
+xfoox xbarx xbazx
+```
+
## Examples
### Config based settings
@@ -172,5 +236,35 @@ conf-y: default foo bar
libs-y: libdef libfoo libbar
```
+### Using `foreach / eval / call` to generate new rules
+```make
+define new_rule
+$(1):
+ @echo "$(1) -> $(2)"
+endef
+
+arg-rule1 = foo
+arg-rule2 = bar
+
+RULES = rule1 rule2
+
+all: $(RULES)
+
+$(foreach R,$(RULES),$(eval $(call new_rule,$(R),$(arg-$(R)))))
+
+# equivalent to
+# $(eval $(call new_rule,rule1,foo))
+# $(eval $(call new_rule,rule2,bar))
+```
+Outputs:
+```text
+rule1 -> foo
+rule2 -> bar
+```
+> Use `make -R -p` to print the make database including the rules.
+
[make-var-override]: https://www.gnu.org/software/make/manual/html_node/Overriding.html
[make-patsubst]: https://www.gnu.org/software/make/manual/html_node/Text-Functions.html#index-patsubst-1
+[make-call]: https://www.gnu.org/software/make/manual/html_node/Call-Function.html
+[make-eval]: https://www.gnu.org/software/make/manual/html_node/Eval-Function.html
+[make-foreach]: https://www.gnu.org/software/make/manual/html_node/Foreach-Function.html