Question

I have the following code in my Makefile, but I get the error mentioning that O?=2 is not a command that sh -c can run. What am I doing wrong here?

gcc:
    O?=2
    @if test -z "$(DEBUG)" ; then \
      g++ -O${O} *.c -o palindrome ; \
    fi

I am trying to set O to 2 if the user did not provide it, and then build my palindrome executable.

---

Exact error:

$ make gcc
O?=2
/bin/sh: O?=2: command not found
make: *** [gcc] Error 127
$

Answer 1

Move it outside the command, so that it gets processed by “make” instead of the shell:

O?=2
gcc:
    @if test -z "$(DEBUG)" ; then \
      g++ -O${O} *.c -o palindrome ; \
    fi