Make error: missing separator

As indicated in the online manual, the most common cause for that error is that lines are indented with spaces when make expects tab characters.

Correct

target: 
\tcmd

where \t is TAB (U+0009)

Wrong

target:
....cmd

where each . represents a SPACE (U+0020).

This is a syntax error in your Makefile. It's quite hard to be more specific than that, without seeing the file itself, or relevant portion(s) thereof.

In my case, I was actually missing a tab in between ifeq and the command on the next line. No spaces were there to begin with.

ifeq ($(wildcard $DIR_FILE), )
cd $FOLDER; cp -f $DIR_FILE.tpl $DIR_FILE.xs;
endif

Should have been:

ifeq ($(wildcard $DIR_FILE), )
<tab>cd $FOLDER; cp -f $DIR_FILE.tpl $DIR_FILE.xs;
endif

Note the <tab> is an actual tab character

In my case, this error was caused by the lack of a mere space. I had this if block in my makefile:

if($(METHOD),opt)
CFLAGS=
endif

which should have been:

if ($(METHOD),opt)
CFLAGS=
endif

with a space after if.

In my case, the same error was caused because colon: was missing at end as in staging.deploy:. So note that it can be easy syntax mistake.

I had the missing separator file in Makefiles generated by qmake. I was porting Qt code to a different platform. I didn't have QMAKESPEC nor MAKE set. Here's the link I found the answer:

https://forum.qt.io/topic/3783/missing-separator-error-in-makefile/5

Just to add yet another reason this can show up:

$(eval VALUE)

is not valid and will produce a "missing separator" error.

$(eval IDENTIFIER=VALUE)

is acceptable. This sort of error showed up for me when I had an macro defined with define and tried to do

define SOME_MACRO
... some expression ...
endef

VAR=$(eval $(call SOME_MACRO,arg))

where the macro did not evaluate to an assignment.

I had this because I had no colon after PHONY

Not this,

.PHONY install
install:
    install -m0755 bin/ytdl-clean /usr/local/bin

But this (notice the colon)

.PHONY: install
...

So apparently, all I needed was the "build-essential" package, then to run autoconf first, which made the Makefile.pre.in, then the ./configure then the make which works perfectly...