i hope you'll get my point here :)
without piping the command is:
aircrack-ng handshakes.cap -w wordlist.txt
redirecting crunch stdout to aircrack:
these commands are not working:
crunch 8 8 abc123 | aircrack-ng handshakes.cap -w -
crunch 8 8 abc123 | aircrack-ng handshakes.cap -w-
crunch 8 8 abc123 | aircrack-ng handshakes.cap -w
crunch 8 8 abc123 | aircrack-ng -w "-" handshakes.cap