Generating Custom Wordlists Using John The Ripper

Recently I used John the Ripper to generate a very specific custom wordlist based on a specific mask.

./john --stdout --mask=?1?1?1?1?1 -1=[a-z0-9]
Press 'q' or Ctrl-C to abort, almost any other key for status
aaaaa
baaaa
caaaa
daaaa
eaaaa
faaaa
gaaaa
haaaa
...

Question mark sets the position, the number 1 sets the "variable", which you then specify afterwards. You can have multiple "variables":

./john --stdout --mask=?1?1?1?1?1?2 -1=[a-z0-9] -2=4
Press 'q' or Ctrl-C to abort, almost any other key for status
aaaaa4
baaaa4
caaaa4
daaaa4
eaaaa4
faaaa4
gaaaa4
haaaa4
iaaaa4
jaaaa4