How to print progressbar when redirecting output to file?

[c19]

I'm using this to run my program: nohup ./target/release/main > main.log &.

But this cause all the progressbars are gone from the logfile. Any method to preserve it?

[chris-laplante]

I don't think there is anything built-in to indicatif to support this. You may however give unbuffer (https://linux.die.net/man/1/unbuffer) a try. That might do what you want.

[djc]

indicatif more or less inherits this behavior from the console crate which it uses under the cover. An indicatif ProgressDrawTarget can be initialized using a caller-provided console::Term (but a cursory reading of the console API did not allow me to find an option to override their detection of whether the used file descriptor is a terminal).

[nyurik]

@djc I think most of the CLI apps are also used in non-interactive (headless?) mode, and could use some support from indicatif. Even without the auto-detection support, would it make sense to have a "linear log" formatter? It could print current status: 5% out of 100% style messages instead of using ansi control characters once per (second/minute/10min/...?). I have seen this behavior with aria2c, wget, and possibly others.

[djc]

Well, if someone wants to propose a design for something like that I'd be willing to review it.

[spoutn1k]

I believe in both this issue and #651 the root problem cause has not been explained.

Bar printing works by printing special characters to control the cursor position on a tty and overwrite previous output. The bar, in most cases, gets redrawn over and over and that gives the illusion of movement.

This is a special property of the virtual terminal you are using. When the output is redirected to a file, docker log, or anything other than a tty, those properties are gone. What you would see is a very long line of partial bars separated by \r characters. This is also true for colors, styling, and other terminal features.

This is not an indicatif issue. This is a consequence of the design of computer systems.

Indicatif seems to refresh 15 times a second. Even if you change the behaviour to write the bar line per line, if your process takes 1mn you have ~900 lines of just bar in your output, cluttering any kind of log or file you are producing. At this point you really need to ask yourself if a bar is needed.

You can do this check yourself and change the behaviour of your program to print differently when the output is not a terminal. @nyurik's suggestion is the best possible way to go about this in indicatif, but I wanted to make sure everybody is on the same page about why indicatif stops working sometimes when I pipe to a file.

[djc]

@spoutn1k thanks for making the additional context explicit.