.if and Makefile issues

[Gary Aitken]

Bewildered and frustrated, looking for some guidance on a seemingly
simple task: check the existence of a file and rename it.

Looking at a number of examples in the Porter's guide, I should be
able to do something like this:

post-build:
<ht>echo "***** post-build *****"
#<ht>Avoid executable name conflict with dcraw port
<ht>.if exists ${WRKSRC}/dcraw
<ht>echo ===== dcraw exists =====
<ht>mv ${WRKSRC}/dcraw ${WRKSRC}/${PORTNAME}-dcraw
<ht>.else
<ht>echo ===== dcraw does not exist =====
<ht>.endif

That causes:
echo "***** post-build *****"
***** post-build *****
.if exists /usr/ports/graphics/ufraw-devel/work/ufraw-6d3259a/dcraw
make[1]: exec(.if) failed (No such file or directory)
*** Error code 1

I then tried adding parens:

post-build:
<ht>echo "***** post-build *****"
#<ht>Avoid executable name conflict with dcraw port
<ht>.if exists(${WRKSRC}/dcraw)
<ht>echo "===== dcraw exists ====="
<ht>mv ${WRKSRC}/dcraw ${WRKSRC}/${PORTNAME}-dcraw
<ht>.else
<ht>echo "===== dcraw does not exist ====="
<ht>.endif

echo "***** post-build *****"
***** post-build *****
.if exists(/usr/ports/graphics/ufraw-devel/work/ufraw-6d3259a/dcraw)
Syntax error: "(" unexpected
*** Error code 2

I finally got this to do *something*:

post-build:
<ht>echo "***** post-build *****"
#   Avoid executable name conflict with dcraw port
.if exists ${WRKSRC}/dcraw
echo ===== dcraw exists =====
mv ${WRKSRC}/dcraw ${WRKSRC}/${PORTNAME}-dcraw
.else
<ht>echo ===== dcraw does not exist =====
.endif

echo "***** post-build *****"
***** post-build *****
echo "===== dcraw does not exist ====="
===== dcraw does not exist =====

Unfortunately, the file *does* exist.

Can someone enlighten me as to what is going on in the above three
situations, to further my education?
Any hints / pointers would be much appreciated:

1. Why does the .if, .else, and .endif have to have no leading whitespace?
2. Why does it require the <ht> on the stmt after the else but not
    after the .if?  (Same behavior with tabs on the ones after .if)
3. Why doesn't it find the file?
4. What's a right way to do this?

# ls /usr/ports/graphics/ufraw-devel/work/ufraw-6d3259a/dcraw
/usr/ports/graphics/ufraw-devel/work/ufraw-6d3259a/dcraw

Thanks, off to sleep to try to save what little hair is left.
Gary