Feature: «batch» mode to print values to stdout

[p4tpr0]

Hello,

I would love having a «batch» mode to print output of ztop to stdout, in a machine-parsable way.
Unfortunately I can’t code…
Great tool anyway. It fills a gap between zpool iostat and top -m io.

[penryu]

Just another ztop fan here, but it's worth noting that all this information is already available in machine-parseable form via systctl kstat.zfs.*.dataset (FreeBSD) or /proc/spl/kstat/zfs/*/objset-*.

That said, it doesn't look like it would be too much trouble to just dump a single tick of tab-separated data to stdout if stdout isn't a tty. I'm tinkering with this in a branch now; nothing fancy, just emitting the pre-filtered, tab-separated values from app.elements() and exiting. This would have the advantage of being a cross-platform way to source the platform-specific information, while using the same filtering as the full ztop UI.

I can prepare an MR if @asomers thinks this sounds like a good idea.

[asomers]

That would definitely have some uses. My only reservation is whether the UI would be general enough to satisfy most users. If not, would it be a better idea to split the app.rs file and its submodules into a separate crate?

[penryu]

There is some behavior in App that could be decoupled for this, namely things like data filtering/sorting (-c, -d, -f, -r, -s) from UI logic like -a / -t. (Some of those would be easier to decouple than others.)

I'm not sure if that's worth a whole new crate though... unless you're considering something like a dual lib/bin setup? Though even that could be done with just a [[bin]] section in the Cargo.toml. What are you thinking?