Make functions manipulate strings and lists. Common ones: wildcard, patsubst, subst, filter, foreach.

wildcard expands a glob pattern to a list of files:

SRCS = $(wildcard *.c)         # main.c util.c helper.c
OBJS = $(patsubst %.c, %.o, $(SRCS))  # main.o util.o helper.o

$(wildcard *.c) lists all .c files in the current directory. Essential for avoiding hardcoded file lists.

patsubst replaces a pattern in a list:

SRCS = main.c util.c
OBJS = $(patsubst %.c, %.o, $(SRCS))   # replaces .c with .o

Syntax: $(patsubst pattern, replacement, list). Replace %.c with %.o in the list.

subst replaces a substring:

SRCS = main.c util.c
OBJS = $(subst .c, .o, $(SRCS))        # simple replacement

Unlike patsubst, subst doesn't use patterns—it replaces the exact string.

filter selects items matching a pattern:

SOURCES = main.c util.c test.h helper.c
C_FILES = $(filter %.c, $(SOURCES))    # main.c util.c helper.c

$(filter %.c, ...) keeps only .c files.

filter-out removes items matching a pattern:

ALL_OBJS = main.o util.o test.o
REAL_OBJS = $(filter-out test.o, $(ALL_OBJS))  # excludes test.o

foreach loops over a list:

DIRS = src lib test
$(foreach DIR, $(DIRS), $(DIR)/Makefile)    # expands to src/Makefile lib/Makefile test/Makefile

shell runs a shell command and captures output:

VERSION = $(shell git describe --tags)
HOSTNAME = $(shell hostname)
 
all:
	@echo "Building version $(VERSION) on $(HOSTNAME)"

$(shell ...) runs the command and uses its output. Useful for dynamic values.

if for conditional expansion:

PLATFORM = $(if $(findstring Linux, $(shell uname)), linux, other)

$(if condition, then, else) expands to then if condition is non-empty, else else.

Chaining functions:

SRCS = $(wildcard src/*.c)
OBJS = $(patsubst src/%.c, build/%.o, $(SRCS))

Read from inner to outer: wildcard finds .c files, patsubst transforms paths. Powerful when combined.

Performance note: Functions like shell are expensive (spawn a process). Avoid calling them in hot loops or on every recipe. Use them sparingly in variable definitions (set once).