Recently I wrote an entry about a simple but difficult wish I had for a certain sort of terminal pager that handled emoji . In comments, people suggested that the venerable less would do what I wanted, which was something I'd already tried and discovered it had behavior I didn't want. Except, well, let me quote my eventual comment:

It turns out that my testing of less's behavior was being contaminated by my usual $LESS settings, and I think that ' less -XRn ' does more or less what I want (I was being fooled partly because my usual $LESS includes 'c', well, technically 'C').

I've been using less for a long time and for most of that time I've had the same set of less settings, burned into a $LESS environment variable set in my dotfiles, and also the same set of alternate less key bindings (where N and P move through files instead of their normal actions). I had long since forgotten the specifics of my $LESS settings when I tested less ; my settings were just how less worked. And so I was fooled into initially thinking that less didn't work for what I wanted.

(I remember N and P partly because when I use less as root or on a machine I haven't particularly set up my account on, I don't have them and I miss them.)

My $LESS setting is far from the only environment variable I have set in my dotfiles. Without looking through them carefully I couldn't tell you what I have set, why I set them that way, and whether or not they're still correct or useful. The same is true for the configuration files for various programs, where I'm sure that surprising things lurk.

(This isn't the first time I've had old personal dotfiles cause problems .)

This is of course just the personal manifestation of a general problem we have in system administration. We set up a lot of settings and configurations that make sense and work at the time, and then we forget about them because they're in the background, just doing what we expect. They can readily become our mental image of how the program or system behaves, because it's certainly how it behaves for us. Then someday either they clash with what we want to do (as my standard $LESS did) or they don't work any more because things changed out from underneath them ( cf ).

I don't have any good answers to this. Some people will advocate not changing any settings from the defaults, but not only is that giving yourself countless little papercuts over time, it doesn't even necessarily protect you; programs can change their default behavior so something you've become accustomed to doesn't work any more.

(It's good to document the settings and why you made them, but that only helps with half of the problem. It's still easy to forget that you even have custom settings. Should you budget an hour every six months or whatever to look over and check your settings? Well, you can put it on the calendar, but I don't think it's going to work in practice, not after the first few times, because it's boring.)