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Assorted less(1) tips

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Re: Assorted less(1) tips

#21

Post by CBLT »

teeray wrote: post #5

Surprised they missed follow! It’s a bit odd to use, but once you get used to it it’s better than tail in many circumstances IMO. `less +F` starts less following stdin or whatever file argument you’ve provided. breaks following, allowing you to search around a business-as-usual `less` session. Hitting `F` (that’s uppercase) starts following again. Yes, you can just start following within a session with `F` too if you…

If you're following a pipe (such as `kubectl logs | less +F`), is sent to all processes in a pipeline, so it stops less from following and it stops the other process entirely. Then you can't start following again with F, or load more data in with G.

Less provides an alternative of to stop following, but that is intercepted by most shells.

Re: Assorted less(1) tips

#22

Post by gerdesj »

layer8 wrote: post #12
teeray wrote: post #5

Surprised they missed follow! It’s a bit odd to use, but once you get used to it it’s better than tail in many circumstances IMO. `less +F` starts less following stdin or whatever file argument you’ve provided. breaks following, allowing you to search around a business-as-usual `less` session. Hitting `F` (that’s uppercase) starts following again. Yes, you can just start following within a session with `F` too if you…

It would be nice to have a mode that follows in the sense of automatically picking up new output, but that simultaneously would let you navigate around, similar to how terminals behave. Then you’d only need an autoscroll toggle for when you’re at the bottom.

Take a look at "lnav" ...

Re: Assorted less(1) tips

#23

Post by GuB-42 »

> The ! lets you invoke an external command.

Also useful for privilege escalation...

If a script running as root uses less (or vi), just do "!bash" and you have a root shell. Note that systems that let you do this are usually pretty weak, and there are often many other ways to get root access, but this is a particularly simple one that I used a few times in the past.

Re: Assorted less(1) tips

#24

Post by teeray »

joombaga wrote: post #19
teeray wrote: post #5

Surprised they missed follow! It’s a bit odd to use, but once you get used to it it’s better than tail in many circumstances IMO. `less +F` starts less following stdin or whatever file argument you’ve provided. breaks following, allowing you to search around a business-as-usual `less` session. Hitting `F` (that’s uppercase) starts following again. Yes, you can just start following within a session with `F` too if you…

With `tail` you can press enter a few times to put some empty lines after the last line. This is useful e.g. when you trigger a function multiple times and want to easily see line groups from each attempt. It's the only reason I still use `tail` for following when `less` is available.

A visual mark would be nice, agreed. I haven't tried it, but I wonder if you could approximate it with the bookmarking feature that less(1) does have. It wouldn't be visible, but it would scroll to a consistent mark.

Re: Assorted less(1) tips

#26

Post by jlokier »

Izkata wrote: post #9
JayGuerette wrote: post #4

Also -X or --no-init " ... desirable if the deinitialization string does something unnecessary, like clearing the screen." I prefer to not clear the screen. I usually want to continue to refer to something or even copy/paste from the content to my current command line.

And combined with -E, it'll quit immediately if the output is smaller than the terminal size. ...And combined with some of the other options in the post, my go-to has been "less -SEXIER" for a long time. Specifying E twice doesn't seem to do anything except make this easier to remember.

I recommend -FX instead of -EX. They both quit immediately if the output is smaller than the screen size, but -FX does not quit if the output is larger and you jump to the end of a large file, so you can continue to do things like scroll back or search.

git uses "less -FRX" by default. This is how I learned about -F.

(To be pedentic, git uses "LESS=FRX less", which accomplishes the same thing.)

Re: Assorted less(1) tips

#28

Post by xg15 »

teeray wrote: post #5

Surprised they missed follow! It’s a bit odd to use, but once you get used to it it’s better than tail in many circumstances IMO. `less +F` starts less following stdin or whatever file argument you’ve provided. breaks following, allowing you to search around a business-as-usual `less` session. Hitting `F` (that’s uppercase) starts following again. Yes, you can just start following within a session with `F` too if you…

Maybe OT, but I thought for a long time that "follow" was some sophisticated file descriptor trickery that required you to somehow "stream" the file while reading and would therefore be incompatible with opening a file "normally".

My mind was blown when finding out its really just "keep on polling after EOF". Meaning there is absolutely no difference between opening a file normally and "following" a file - and software could easily switch between the two "modes" on the fly.

Re: Assorted less(1) tips

#29

Post by vladvasiliu »

teeray wrote: post #24
joombaga wrote: post #19

Earlier quoted context omitted.

With `tail` you can press enter a few times to put some empty lines after the last line. This is useful e.g. when you trigger a function multiple times and want to easily see line groups from each attempt. It's the only reason I still use `tail` for following when `less` is available.

A visual mark would be nice, agreed. I haven't tried it, but I wonder if you could approximate it with the bookmarking feature that less(1) does have. It wouldn't be visible, but it would scroll to a consistent mark.

I usually use tail when I need to do some ad-hoc log following.

Having to set bookmarks and remember them is a PITA I can usually do without. If I'm looking at "normal" log output, it's usually set up in a nice aggregator somewhere, where I can easily exclude noise and otherwise uninteresting output.

Re: Assorted less(1) tips

#30

Post by osmsucks »

btdmaster wrote: post #8

You can also press `s` to save data from a pipe to a file rather than manually copy pasting.

I came here to suggest the same! It's incredibly handy and I use it all the time at work: there's a process that runs for a very long time and I can't be sure ahead of time if the output it generates is going to be useful or not, but if it's useful I want to capture it. I usually just pipe it into `less` and then examine the contents once it's done running, and if needed I will use `s` to save it to a file.

(I suppose I could `tee`, but then I would always dump to a file even if it ends up being useless output.)

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