How do I perform arithmetic in a makefile?

Question

Is it possible to perform some operations on variables in a makefile? For instance, defining

JPI=4
JPJ=2

is it possible to define in the same makefile a variable JPIJ equal to the expanded value of $(JPI)*$(JPJ)?

Flow · Accepted Answer · 2014-02-03 12:47:05Z

51

Using Bash arithmetic expansion:

SHELL=/bin/bash
JPI=4
JPJ=2
all:
    echo $$(( $(JPI) * $(JPJ) ))

The first line is to choose the Bash shell instead of the default (sh). Typically, sh doesn't support arithmetic expansion. However in Ubuntu, /bin/sh is provided by Dash, which supports this feature. So that line could be skipped.

The double dollar sign is because we want the expansion to be done by the shell. Note: the JPI and JPJ variables are expanded by make first, then the expression is passed to bash like this:

$(( 4 * 2 ))

edited Feb 3, 2014 at 12:47

Flow

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answered Apr 12, 2013 at 18:23

Dominic

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3 Comments

Søren Løvborg Over a year ago

POSIX sh does indeed support arithmetic expansion.

Flow Over a year ago

+1 as this is the best solution because it only depends on a POSIX compatible shell. And thanks for pointing out that we need a double dollar sign when doing shell arithmetic in make.

xdevs23 Over a year ago

If you want to do arithmetic outside of a build rule, for example, to assign a variable, you can use: RESULT := $(shell echo $$(($(JPI) * $(JPJ))))

Jean-Francois T. · Accepted Answer · 2015-12-30 09:49:17Z

23

Answer from @mrkj is great but as @Daniel mentions, not all systems have bc (for example, I don't have it on MSys).

I have found the two following methods, both using shell: $$(( ... )) and expr ...

JPI=4
JPJ=2

#With Double-dollar
JPIJ_1 = $(shell echo $$(( $(JPI) + $(JPJ) )))

#With 'expr'
JPIJ_2 = $(shell expr $(JPI) + $(JPJ) )

$(info Sum with Double-$$: $(JPIJ_1))
$(info Sum with 'expr': $(JPIJ_2))

Note that when using expr, you shall put spaces around the + or it will return 4+2. This is not required when using $$.

.

When you have bc available, you might definitely go with it. I found the following page very interesting: http://www.humbug.in/2010/makefile-tricks-arithmetic-addition-subtraction-multiplication-division-modulo-comparison/

edited Dec 30, 2015 at 9:49

answered Dec 30, 2015 at 9:34

Jean-Francois T.

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1 Comment

Arne L. Over a year ago

Beware that expr ... is executed by your shell and, thus, is subject to name expansion, e.g. expr 2 * 3 will cause an error instead of the expected output because * is expanded by the shell to all file names in the current directory. You will need to either escape the operator expr 2 \* 3 or put the whole expression in single quotes expr '2 * 3'.

mrkj · Accepted Answer · 2009-12-18 03:32:19Z

18

If you're using GNU make and have bc installed on your system, you can use something like this:

JPI=4
JPJ=2
FOO=$(shell echo $(JPI)\*$(JPJ) | bc)
all:
  echo $(FOO)

answered Dec 18, 2009 at 3:32

mrkj

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2 Comments

Daniel Alder Over a year ago

expr is more common than bc: $(shell expr $(JPI) \* $(JPJ))

mrkj Over a year ago

@DanielAlder: Interesting, I always use bc but I can see how expr is possibly more convenient if you're doing simple base 10 integer arithmetic (which is the case for this question).

Eric Melski · Accepted Answer · 2009-12-18 07:14:30Z

11

It's clumsy (or brilliant, depending on your perspective), but you can do arithmetic directly in GNU make. See Learning GNU Make Functions with Arithmetic. Be aware though that this method doesn't scale well. It will work wonderfully for small numbers as you have shown in your question, but it doesn't do well when you're working with numbers with a large magnitude (greater than 10,000,000).

answered Dec 18, 2009 at 7:14

Eric Melski

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2 Comments

Kamath Over a year ago

hmmm.... its surprising to see makefiles can do math. Shouldn't this be a easy feature to add ?

Vroomfondel Over a year ago

@Kamath take a look at gmtt to find an implementation for big numbers (~63 places but you could have more if you want). The code is still clumsy or maddening or awkward or scary, depending on your perspective, tho

ruvim · Accepted Answer · 2021-03-14 13:27:45Z

10

In GNU Make with Guile support (i.e. since version 4.0) it is easy to use call to Scheme language for arithmetic or other calculations. It is done without creating any subshell or child process.

An example

JP-I := 4
JP-J := 2
JP-IJ := $(guile (* $(JP-I) $(JP-J) ))

$(info JP-IJ = $(JP-IJ) )
# prints: JP-IJ = 8

See also the manual for Guile Arithmetic Functions.

A possible check for Guile:

ifeq (,$(filter guile,$(.FEATURES)))
  $(error Your Make version $(MAKE_VERSION) is not built with support for Guile)
endif

edited Mar 14, 2021 at 13:27

answered Aug 16, 2017 at 13:24

ruvim

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1 Comment

Hotschke Over a year ago

Under macOS you can install GNU Make with Guile support via MacPorts: $ sudo port install gmake +guile.

Matthew Simoneau · Accepted Answer · 2025-02-05 15:03:01Z

5

The GNU Make Standard Library provides integer arithmetic functions.

include gmsl

JPI = 4
JPJ = 2

JPIJ = $(call plus,$(JPI),$(JPJ))

edited Feb 5, 2025 at 15:03

answered Jan 7, 2014 at 6:05

Matthew Simoneau

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3 Comments

jww Over a year ago

Oh man... I saw this and thought GREAT, something built it without hacks. Then I noticed its a SourceForge project, and the project just hijacked the name and added some hype.

yyny Over a year ago

@MatthewSimoneau 'GNU'

Matthew Simoneau Over a year ago

@YoYoYonnY, it is a "standard library" for GNU Make. I can see how "standard library" is a bit bold, but the "GNU Make" part is just descriptive.

Vroomfondel · Accepted Answer · 2018-10-09 07:48:46Z

To add a late answer to the pool: The GNUmake table toolkit features many arithmetic functions. You can add, subtract, multiply, divide, take the modulus in base 8,10 and 16. Also there are the usual binary operations and, or, xor and not. Numbers can be around 60 digits but you can adapt this, if you need more. The code is pure GNUmake syntax and therefore portable between Windows and Unix, contrary to shell scripts - in case you want to number crunch, there may be better solutions ;) of course.

Here is an example:

include gmtt/gmtt.mk

NUMBER_A := -12392834798732429827442389
NUMBER_B := 984398723982791273498234
$(info $(call add,$(NUMBER_A),$(NUMBER_B)))
$(info $(call sub,$(NUMBER_A),$(NUMBER_B)))
$(info $(call mul,$(NUMBER_A),$(NUMBER_B)))
$(info $(call div,$(NUMBER_A),$(NUMBER_B)))
$(info $(call mod,$(NUMBER_A),$(NUMBER_B)))

Output:

$ make
-11408436074749638553944155
-13377233522715221100940623
-12199490762401735834920873237276176262117128241026
-12
-580050110938934545463581

Ayberk Özgür · Accepted Answer · 2023-01-13 13:20:22Z

1

After an hour of hair pulling, I ended up on this (assuming you got hexadecimal and decimal numbers mixed in like my use case):

JPI = 0x123
JPJ = 2
MUL = $(shell python3 -c "print($(JPI)*$(JPJ))")

answered Jan 13, 2023 at 13:20

Ayberk Özgür

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2 Comments

Teque5 Over a year ago

Hilarious make is so crummy we have to resort to this...

Ayberk Özgür Over a year ago

Nobody uses human-written Makefiles anymore if they can avoid it, and for good reason

Daniel · Accepted Answer · 2012-12-29 20:12:04Z

0

With makepp it's much easier. You get direct access to the underlying Perl interpreter. In this case the makeperl function does variable expansion before evaluating as Perl, the perl function OTOH would only evaluate:

JPI=4
JPJ=2
JPIJ = $(makeperl $(JPI)*$(JPJ))
&echo result: $(JPIJ)

You can use the builtin &echo command outside of a rule as a statement.

answered Dec 29, 2012 at 20:12

Daniel

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