explain $@, $<, $1 with examples

In Makefile, the special variables $@, $<, and $1 are used to represent different parts of the rule being executed. Here's what each of them means and how they are used:

1. $@
- $@ represents the target file name. It is used to reference the file name of the target being built. For example:

main: main.o utils.o
    gcc -o $@ $^

In this example, $@ refers to the target file name `main`, and $^ refers to the list of dependencies (`main.o` and `utils.o`).

2. $<
- $< represents the first dependency file name. It is used to reference the first dependency in the list of dependencies. For example:

main.o: main.c
    gcc -c $<

In this example, $< refers to the first dependency file name `main.c`.

3. $1
- $1 represents a variable that is defined by the user. It is used to reference the value of the first argument passed to a makefile target. For example:

.PHONY: build
build:
    echo "Building $1"

In this example, `build` is a target that expects an argument. When called like `make build arg=value`, the value of the argument is referenced using $1.