You can do a lot worse than ACH. It's hard to read, but it's simple and pretty well-defined.
What _really_ sucks is one-off fixed-width formats that aren't well defined, or that change suddenly (oh, you thought that field would always be populated? lol no.)
Yeah, ACH is surprisingly not-unpleasant, at least relative to nightmares like X12 EDI with its implicit looping constructs and billions of companion guides that supercede random parts of the base spec.
X12 EDI, been there earned the badge, both on the generating and receiving sides. 837, 834, 835 and others in health care - fun! Positional format, with situational meaning... really it is a fascinating format.
i wrote the X12 EDI stuff for a major clearwater distributor... also wrote the ACH stuff that dumped someone a file and their job was to upload it via SFTP to the bank. so many badges.
What _really really_ sucks is well-defined, reasonable, meticulously documented formats where all in-the-wild implementations stray from the spec in different ways :-/
What _really_ sucks is one-off fixed-width formats that aren't well defined, or that change suddenly (oh, you thought that field would always be populated? lol no.)