Fragment of a `./configure.sh` I wrote that generates a `build.ninja`

configure.sh

#!/bin/bash
# shellcheck disable=SC2016 # Dollar signs in single quotes are destined to Ninja, not Bash.
# Safety belt, even if not perfect. Combined with Shellcheck, we should be okay.
set -euo pipefail

cd "$(dirname "$0")" # Go to the script's directory.

BUILD_DIR="build"

CFLAGS="-D_GNU_SOURCE -pthread $(pkg-config --cflags sdl2)"
INC_PATHS=(
    src/evdev/include/
)
LDFLAGS="-Wl,-z,defs $(pkg-config --libs-L-only sdl2)"
LDLIBS="$(pkg-config --libs-l-only sdl2)"

SOURCE_ID_LIST_C="$BUILD_DIR/src_id_list.c"

SRCS=(
	src/main.c
	src/stuff.c

    src/evdev/evdev.c

	"$SOURCE_ID_LIST_C"
)

readonly BUILD_DIR CFLAGS INC_PATHS LDFLAGS LDLIBS SOURCE_ID_LIST_C SRCS


# Configuration time!

declare -A OBJS
for src in "${SRCS[@]}"; do
	OBJS[$src]="$BUILD_DIR/$(basename "$src" .c).o"
done
typeset -r OBJS


gen_src_id_list() {
    printf 'char const * src_id_list[] = {\n'
    for src in "${SRCS[@]}"; do
        printf '\t"%s",\n' "${src//\"/\\\"}"
    done
    printf '};\n'
}
gen_src_id_list >"$SOURCE_ID_LIST_C"


# File generation functions.

new_file() {
	# We will write to a temp file, which we will then move atomically.
	# This will avoid problems if several processes try to write to the file at the same time.
	TMP_FILE=$(mktemp -p "$BUILD_DIR")
	FINAL_FILE="$1"
	# shellcheck disable=SC2064 # `@Q` ensures the expansion is reusable as input.
	trap "rm -f ${TMP_FILE@Q}" EXIT
}
file_done() {
	# Atomically overwrite the original file.
	mv "$TMP_FILE" "$FINAL_FILE"
	trap - EXIT # Reset the deletion trap.
}

print() {
	# shellcheck disable=SC2059 # The first argument is intentionally a format.
	printf "$@" >> "$TMP_FILE"
}
println() {
	print "$1\n" "${@:2}"
}
empty_line() {
	println ''
}


# `build.ninja` generation functions.

new_file build.ninja

variable() { # variable <name> <value>
	println "%s = %s" "$1" "$2"
}

# The command will be interpreted by the shell,
# so variables should be expanded with `${var@Q}` rather than `$var`.
rule() { # rule <name> <cmd> [<descr> [<variables>...]]
	println "rule %s" "$1"
	println "    command = %s" "$2"
	if [[ $# -ge 3 ]]; then
		println "    description = %s" "$3"
		for var in "${@:4}"; do
			println "    $var"
		done
	fi
}

# Paths passed to this function should have their spaces escaped (`$ `);
# variables that will be used in the command should follow the same precautions as for `rule`.
build() { # build <products> <rule name> <inputs> [<variables...]
	println "build %s: %s %s" "$1" "$2" "$3"
	for var in "${@:4}"; do
		if [ -n "${var/ }" ]; then
			println "    %s" "$var"
		fi
	done
}


# 1.2 required for `ninja_required_version`.
# 1.3 required for `deps =`.
# 1.7 required for implicit outputs.
println 'ninja_required_version = 1.7'

empty_line

println '# Special variable for Ninja'
variable builddir "${BUILD_DIR/ /\$ }"

empty_line

rule configure './$in' 'Re-configuring...'
println '    generator = true'
build "build.ninja ${SOURCE_ID_LIST_C/ /\$ } \$builddir/compile_commands.json" configure configure.sh

empty_line
empty_line


# Variable definitions.

variable cc "$CC"
variable ar "$AR"

empty_line

INC_FLAGS=()
for path in "${INC_PATHS[@]}"; do
	INC_FLAGS+=(\$$'\n'\"-I"$path"\")
done
variable cflags "$CFLAGS ${INC_FLAGS[*]}"

empty_line

variable ldflags "$LDFLAGS"

empty_line

variable ldlibs "$LDLIBS"


empty_line
empty_line


# Rules.

rule cc '$cc $cflags -c $in -o "$out" -MD -MP -MF "$out.d"' 'CC $in' 'depfile = $out.d' 'deps = gcc'
empty_line
rule link '$cc $cflags $ldflags $in -o "$out" $ldlibs' 'LINK $out'
empty_line
rule staticlib '$ar rcs "$out" $in' 'STATIC LIB $out'


empty_line
empty_line


# Builds.

build all phony "\$builddir/${NOM_APP/ /\$ }"
build "\$builddir/${NOM_APP/ /\$ }" link "${OBJS[*]/ /\$ }"

for src in "${SRCS[@]}"; do
	build "${OBJS[$src]}" cc "$src" "cflags = \$cflags  -DFILE_NAME=${src@Q}"
done