Identify the direction of lines in an ASCII-figure
Slip, 6 + 2 = 8 bytes

+2 bytes for the f flag.

^*`#`#


Try it here!

Prints one of the following:

##




#
#




# 
 #




 #
# 


Explanation

The ^* sets the IP's direction to any one of the eight octilinear directions. Then `#`# simply matches two hash symbols in that direction. The f flag limits Slip to looking only for the first match, and by default the bounding box of that match is printed to STDOUT.

The pattern itself would be two bytes shorter in Snails (z\#2), but I don't think Snails can print the match itself, it only has numeric output (and adapting the pattern to printing 4 different numbers based on the direction would most likely take a lot more bytes).