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Chapter 5: Writing Recipes in Rules 55
‘--warn-undefined-variables’). MFLAGS was traditionally used explicitly in the recursive
make command, like this:
subsystem:
cd subdir && $(MAKE) $(MFLAGS)
but now MAKEFLAGS makes this usage redundant. If you want your makefiles to be compat-
ible with old make programs, use this technique; it will work fine with more modern make
versions too.
The MAKEFLAGS variable can also be useful if you want to have certain options, such as
‘-k’ (see Section 9.7 [Summary of Options], page 104), set each time you run make. You
simply put a value for MAKEFLAGS in your environment. You can also set MAKEFLAGS in a
makefile, to specify additional flags that should also be in effect for that makefile. (Note
that you cannot use MFLAGS this way. That variable is set only for compatibility; make does
not interpret a value you set for it in any way.)
When make interprets the value of MAKEFLAGS (either from the environment or from a
makefile), it first prepends a hyphen if the value does not already begin with one. Then
it chops the value into words separated by blanks, and parses these words as if they were
options given on the command line (except that ‘-C’, ‘-f’, ‘-h’, ‘-o’, ‘-W’, and their long-
named versions are ignored; and there is no error for an invalid option).
If you do put MAKEFLAGS in your environment, you should be sure not to include any
options that will drastically affect the actions of make and undermine the purpose of make-
files and of make itself. For instance, the ‘-t’, ‘-n’, and ‘-q’ options, if put in one of these
variables, could have disastrous consequences and would certainly have at least surprising
and probably annoying effects.
If you’d like to run other implementations of make in addition to GNU make, and hence
do not want to add GNU make-specific flags to the MAKEFLAGS variable, you can add them
to the GNUMAKEFLAGS variable instead. This variable is parsed just before MAKEFLAGS, in
the same way as MAKEFLAGS. When make constructs MAKEFLAGS to pass to a recursive make
it will include all flags, even those taken from GNUMAKEFLAGS. As a result, after parsing
GNUMAKEFLAGS GNU make sets this variable to the empty string to avoid duplicating flags
during recursion.
It’s best to use GNUMAKEFLAGS only with flags which won’t materially change the be-
havior of your makefiles. If your makefiles require GNU make anyway then simply use
MAKEFLAGS. Flags such as ‘--no-print-directory’ or ‘--output-sync’ may be appropri-
ate for GNUMAKEFLAGS.
5.7.4 The ‘--print-directory’ Option
If you use several levels of recursive make invocations, the ‘-w’ or ‘--print-directory’
option can make the output a lot easier to understand by showing each directory as make
starts processing it and as make finishes processing it. For example, if ‘make -w’ is run in
the directory /u/gnu/make, make will print a line of the form:
make: Entering directory ‘/u/gnu/make’.
before doing anything else, and a line of the form:
make: Leaving directory ‘/u/gnu/make’.
when processing is completed.
- GNU Make 1
- Short Contents 5
- Table of Contents 7
- 1 Overview of make 11
- 2 An Introduction to Makefiles 13
- 2.2 A Simple Makefile 14
- 2.6 Another Style of Makefile 18
- 3 Writing Makefiles 21
- 3.1.1 Splitting Long Lines 22
- 3.3 Including Other Makefiles 23
- 3.4 The Variable MAKEFILES 24
- 3.5 How Makefiles Are Remade 24
- 3.7 How make Reads a Makefile 26
- Conditional Directives 27
- Rule Definition 27
- 3.8 Secondary Expansion 28
- 4 Writing Rules 31
- 4.2 Types of Prerequisites 32
- 4.3.1 Wildcard Examples 33
- 4.3.3 The Function wildcard 34
- 4.4.2 The vpath Directive 36
- 4.5 Phony Targets 39
- 4.11 Static Pattern Rules 46
- 4.12 Double-Colon Rules 48
- %.d: %.c 49
- @set -e; rm -f $@; \ 49
- 5 Writing Recipes in Rules 51
- 5.2 Recipe Echoing 53
- 5.3 Recipe Execution 54
- 5.3.2 Choosing the Shell 55
- 5.4 Parallel Execution 57
- 5.5 Errors in Recipes 59
- 5.7 Recursive Use of make 60
- 5.8 Defining Canned Recipes 66
- 5.9 Using Empty Recipes 67
- 6 How to Use Variables 69
- 6.3.1 Substitution References 72
- 6.3.2 Computed Variable Names 73
- 6.5 Setting Variables 75
- 6.7 The override Directive 78
- 6.9 Undefining Variables 79
- 6.13 Suppressing Inheritance 82
- 6.14 Other Special Variables 83
- 7.1 Example of a Conditional 87
- 7.2 Syntax of Conditionals 88
- 8.1 Function Call Syntax 93
- 8.3 Functions for File Names 97
- 8.5 The foreach Function 100
- 8.6 The file Function 101
- 8.7 The call Function 102
- 8.8 The value Function 103
- 8.9 The eval Function 103
- 8.10 The origin Function 104
- 8.11 The flavor Function 105
- 8.14 The guile Function 107
- 8.13 The shell Function 107
- 9 How to Run make 109
- 9.5 Overriding Variables 113
- 9.7 Summary of Options 114
- 10 Using Implicit Rules 121
- 10.4 Chains of Implicit Rules 127
- 10.5.2 Pattern Rule Examples 129
- 10.5.3 Automatic Variables 130
- 10.5.4 How Patterns Match 132
- 10.7 Old-Fashioned Suffix Rules 135
- 12 Extending GNU make 143
- 12.2 Loading Dynamic Objects 145
- 12.2.1 The load Directive 146
- Loaded Object Licensing 147
- Data Structures 148
- Registering Functions 148
- Registered Function Interface 148
- GNU make Facilities 148
- Memory Management 149
- 12.2.4 Example Loaded Object 149
- 13 Features of GNU make 153
- 15 Makefile Conventions 159
- 15.2 Utilities in Makefiles 160
- CFLAGS = -g 161
- ALL_CFLAGS = -I. $(CFLAGS) 161
- Appendix A Quick Reference 175
- Index of Concepts 201
- 192 GNU make 202
- Index of Concepts 193 203
- 194 GNU make 204
- Index of Concepts 195 205
- 196 GNU make 206
- Index of Concepts 197 207
- 198 GNU make 208
- 200 GNU make 210
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