apt-get update apt-get install crunch
Now, just like I mention in John the Ripper | Aircrack-ng that we can use John the Ripper to pipe it's output to aircrack-ng, we can do the same with Crunch. To do this just use the --stdout and | symbol. In the word list option for aircrack-ng just use -w -.
./crunch [minlength] [maxlength] [charset] [options] --stdout | aircrack-ng [options] -w - <file.cap>