Where is this documented? It's not indicated in ld.so's manpage:
http://man7.org/linux/man-pages/man8/ld.so.8.html
Sounds like a bug in GNU's ld.so more than anything.
It's neither unique to glibc (AIX, Solaris) nor to LD_LIBRARY_PATH (PATH), nor trailing colons (leading colons, adjacent colons).
This de facto standard becomes a little more obvious when one considers a likely implementation (iterating over "strchr(arg, ':')" or whatever). Any of these sequences then will give up an empty string:
PATH=:/foo
PATH=/foo:
PATH=/foo::/bar
zwp:/tmp$ cd ''
zwp:/tmp$ pwd
/tmp
zwp:/tmp$
I agree it's surprising and potentially dangerous.
FWIW, the execp() functions hide a similar wtf. From the Linux man page:
The file is sought in the colon-separated list of
directory pathnames specified in the PATH envi‐
ronment variable. If this variable isn't defined,
the path list defaults to the current directory
followed by the list of directories returned by
confstr(_CS_PATH).
http://www.sco.com/developers/gabi/latest/ch5.dynamic.html#s...
The dynamic array tag DT_RUNPATH gives a string that holds a list of directories, separated by colons (:). For example, the string /home/dir/lib:/home/dir2/lib: tells the dynamic linker to search first the directory /home/dir/lib, then /home/dir2/lib, and then the current directory to find dependencies.
The following values would be equivalent to the previous example:
LD_LIBRARY_PATH=/home/dir/usr/lib:/home/dir2/usr/lib:
export FOOBAR=/usr/local/lib
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$FOOBAL