Why parse lines with colons

[Yehoyaqim Martillo]

>One of the reasons /bin/sh (bsh to those who like csh)
>parses lines with ":" in the beginning is because of
>constructs like the following:

>: ${FOO:-default}

>This effectively sets $FOO to a default value if not previously
>set.  

According to my shell manual the value of this expression is $FOO is FOO
is set and not not null otherwise, the value is default.  The value of FOO
does not change.  I believe he means 

: ${FOO:=default}
	
>The longhand way would be:

>if [ "${FOO}" = "" ]
>then
>	FOO=default
>fi

He could just as well have used:

FOO=${FOO:-default}
	
which avoids the ":" and takes hardly any (and probably no) more time to
execute.

-- 

Who wouldn't break for whales?

Yehoyaqim Shemtob Martillo