How to do arithmetic operation in makefile?

Question

I am performing the following in the makefile to measure the time taken in doing some operation:-

START=$(shell date +%s) <br>
@if [ -s mfill.mapi.diff ]; then echo "difference exist between GOLDEN map file and test map file, see mfill.map.diff" ; fi <br>
END=$(shell date +%s) <br>
DIFF_SUB=$(shell echo $(END)\-$(START) | bc) <br>
@echo "It took ${DIFF_SUB} seconds"

It results in following output :-

START=1309941257
END=1309941268
DIFF_SUB=
It took seconds

Could you guys suggest where i did wrong?

possible duplicate http://stackoverflow.com/questions/1926063/arithmetic-in-a-makefile — Fredrik Pihl, Jul 06 '11 at 08:40
@Fredrik: I am too lazy to not saw that post. I went through that post and that didn't work for me. — crazy_prog, Jul 06 '11 at 08:43
@amitesh - If you format code as code (rather than quote) you'll get syntax highlighting as a bonus. — Álvaro González, Jul 06 '11 at 09:17
@Álvaro G. Vicario - Could you please share the procedure of how to do that? — crazy_prog, Jul 06 '11 at 09:27
@amitesh - You can either indent the whole code block (hitting Ctrl+K or copying it already indented) or just use the **{}** toolbar button. — Álvaro González, Jul 06 '11 at 09:32

jcomeau_ictx · Accepted Answer · 2011-07-06T09:30:17.357

1

I don't think you should be using curly braces for Makefile variables: $(END) not ${END}

You want subtraction but you used a '*'.

jcomeau@intrepid:/tmp$ cat Makefile 
START=3
END=5
DIFF_SUB=$(shell echo $(END)-$(START) | bc)
test:
    @echo it took $(DIFF_SUB) seconds
jcomeau@intrepid:/tmp$ make
it took 2 seconds

If you're doing these inside the target, use your curly braces but double $s: $${DIFF_SUB}

jcomeau@intrepid:/tmp$ cat Makefile 
START=3
END=5
DIFF_SUB=$(shell echo $(END)-$(START) | bc)
test:
    @echo it took $(DIFF_SUB) seconds
test2:
    @START=3 && \
    echo HELLO && \
    END=7 && \
    DIFF_SUB=$$(($$END - $$START)) && \
    echo it took $${DIFF_SUB} seconds
jcomeau@intrepid:/tmp$ make test test2
it took 2 seconds
HELLO
it took 4 seconds

edited Jul 06 '11 at 09:30

answered Jul 06 '11 at 08:42

jcomeau_ictx

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works for me, did you change all the curly braces? did you change the asterisk to a minus sign? you've still got curly braces around DIFF_SUB. – jcomeau_ictx Jul 06 '11 at 08:48
I am doing the above operation inside the target. I think it is not creating problem. @ jcomeau_ictx : I did that and edited above but it is not working. – crazy_prog Jul 06 '11 at 08:53
see edited answer. you're still showing curly braces around DIFF_SUB. – jcomeau_ictx Jul 06 '11 at 08:54
wait, if you're doing that inside the target, it's a different story altogether. I'll edit the answer. – jcomeau_ictx Jul 06 '11 at 08:56
2

see revised answer. you're going to run into trouble mixing Make constructs with Bash constructs; use one or the other. – jcomeau_ictx Jul 06 '11 at 09:06
Why you add "&& \" in the end of statements? – crazy_prog Jul 06 '11 at 09:14
@jcomeau_ictx let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/1175/discussion-between-amitesh-and-jcomeau-ictx) – crazy_prog Jul 06 '11 at 09:19
because each line of Bash runs in its own context; the values don't carry on to the next line, it has to be all on one line. – jcomeau_ictx Jul 06 '11 at 09:20
Could you please insert one statement such as "echo HELLO" between "START" and "END" and let it work for me? – crazy_prog Jul 06 '11 at 09:25

How to do arithmetic operation in makefile?

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