Compare two files in makefile

Question

I need help with comparing two files in makefile. I need something like this:

if [cmp $(FILE1) $(FILE2)] !=0; than 
 echo "OK" 
else 
 echo "WRONG" 
fi

But I am not sure how exactly to do that, Thanks

e.dan · Accepted Answer · 2011-04-28T06:24:44.017

7

Edit: corrected mistaken use of -z to -eq 0 and added Makefile context help.

It's really a shell question, not specific to makefiles, but this code would work:

cmp -s $(FILE1) $(FILE2)
RETVAL=$?
if [ $RETVAL -eq 0 ]; then 
    echo "SAME" 
else 
    echo "NOT SAME" 
fi

In a makefile rule, that would look like:

my_compare:
    cmp -s $(FILE1) $(FILE2); \
    RETVAL=$$?; \
    if [ $$RETVAL -eq 0 ]; then \
            echo "SAME"; \
    else \
            echo "NOT SAME"; \
    fi

edited Apr 28 '11 at 06:24

answered Apr 28 '11 at 05:35

e.dan

7,275
1
26
29

I know it would be better in shell but I must do it in makefile. Your code compare files but then on RETVAL there is Error 1. – Libor Zapletal Apr 28 '11 at 05:43
You can do it in a makefile, sure - maybe your question was how to get the shell actions to execute correctly in a makefile rule - that wasn't so clear from the question. If so, see edit. Also note that I corrected the shell code - it had a mistake - oops, sorry. – e.dan Apr 28 '11 at 06:25
I am sorry if I didn´t say it clear but I needed it in a makefile rule. Now it works, thank you – Libor Zapletal Apr 28 '11 at 06:36
@Bibo - it was pretty clear actually - my bad :) glad it helped. – e.dan Apr 28 '11 at 06:58
1

Why don't you test `$?` (i.e., `$$?`) directly? I see no reason to store it in `RETVAL`. Better yet, just execute `cmp` in the `if`: `if cmp -s $(FILE1) $(FILE2); then ...` – Jack Kelly Apr 28 '11 at 09:45
3

@Jack - I agree with putting the `cmp` in the `if` itself - good point. But I have learned from experience to always save the exit status of shell commands in something named `RETVAL` since it avoids those tricky bugs when the next programmer comes along and puts other commands between, not realizing that the `if` was inextricably linked to the last command that was run. Putting it immediately in a variable makes this more obvious (I think) and makes it more maintainable. – e.dan Apr 28 '11 at 11:50
@e.dan re `RETVAL`: I guess that makes sense, but I'd store `RETVAL` on the same line as the command whose `$?` you are capturing. – Jack Kelly Apr 28 '11 at 22:38

score 2 · Answer 2 · answered Apr 28 '11 at 05:32

2

Return code from diff command will be 0 if files are identical, and 1 if files differs.

answered Apr 28 '11 at 05:32

Charles Brunet

21,797
24
83
124

Compare two files in makefile

2 Answers2