What Did Users Do or Use Before the Make Command

The error you're encountering:

*** missing separator (did you mean TAB instead of 8 spaces?). Stop.

Means that the makefile contains spaces instead of Tab's. The make utility is notoriously picky about the use of Space instead of Tab. So it's likely that the makefile contains Space at the beginning of rule stanzas within the file.

Example

Let's say I have the following 3 .c files:

char *
hello() 
{
  return "Hello";
}

char *
world() 
{
  return "world";
}

#include <stdio.h>

/* Prototypes. */
char *hello();
char *world();

int
main(int argc, char *argv[]) 
{
    printf("%s, %s!\n", hello(), world());
    return 0;
}    

Say I have the following Makefile:

# The executable 'helloworld' depends on all 3 object files
helloworld: main.o hello.o world.o
        cc -o helloworld main.o hello.o world.o # Line starts with TAB!

# Build main.o (only requires main.c to exist)
main.o: main.c
        cc -c main.c # Line starts with TAB!

# Build hello.o (only requires hello.c to exist)
hello.o: hello.c
        cc -c hello.c # Line starts with TAB!

# Build world.o (only requires world.c to exist)
world.o: world.c
        cc -c world.c # Line starts with TAB!

#  Remove object files, executables (UNIX/Windows), Emacs backup files, 
#+ and core files
clean:
        rm -rf  *.o helloworld *~ *.core core # Line starts with TAB!

Now we try to build a target

When I run it against the target helloworld:

$ make helloworld
makefile:3: *** missing separator (did you mean TAB instead of 8 spaces?).  Stop.

Look familiar?

Fixing the issue

You can fix this by changing the Spaces to actual Tab characters. I used vim to repair my file. Simply open it:

$ vim makefile

And then run this command within:

:%s/^[ ]\+/^I/

NOTE: ^I is a special character. Typing ^ followed by I will be interpreted differently compared to Ctrl+V-Ctrl+I.

This will substitute all the lines that begin with 1 or more Spaces with an actual Tab.

Now when I rerun my helloworld target:

$ make helloworld
cc -c main.c # Line starts with TAB!
cc -c hello.c # Line starts with TAB!
cc -c world.c # Line starts with TAB!
cc -o helloworld main.o hello.o world.o # Line starts with TAB!

References

• Makefile for hello.c, world.c, and main.c

Make does this using its built-in rules. These tell it in particular how to compile C code and how to link single-object programs.

You actually don't even need a Makefile:

make test

would work without one.

To see the hidden rules that make all of this possible, use the -p option with no Makefile:

make -p -f /dev/null

The -r option disables these built-in rules.

As pointed out by alephzero, Make has had built-in rules for a very long time (if not always); Stuart Feldman's first version in Unix V7 defines them in files.c, and his 1979 paper mentions them. They're also part of the POSIX specification. (This doesn't mean that all implementations of Make support them — the old Borland Make for DOS doesn't, at least up to version 3.0.)