On Sun, Jan 22, 2017 at 8:45 PM Ian Lance Taylor <i...@golang.org> wrote:
> On Sat, Jan 21, 2017 at 4:07 PM, James Aguilar <aguilar.ja...@gmail.com> > wrote: > > If you don't know or care about pagers and process management, you can > stop > > reading now. > > > > Background: I have a program that compile my code each time I modify it. > It > > produces logs continuously on a terminal. > > > > I'm trying to write a go program to wrap this program so that each > compile > > log is opened in a pager, and so that when a new compile starts, the > pager > > for the previous compile is automatically closed. Essentially, I'm > trying to > > change the program from doing (pseudo-shell) > > > > while true; do > > awaitChange > > build > > end > > > > to: > > > > while true; do > > awaitChange > > kill $! > > build | less & # <--- except less should be in the foreground of the > > terminal > > to_kill=$! > > end > > > > There are wrinkles: I don't control the program that executes this loop. > So > > I wrote a go program to process the input and separate it into a series > of > > output buffers based on a regexp. I've gotten it to the point where I can > > start and kill less, and feed it the separated inputs. > > > > My problem: less is not behaving as it would if you ran it on the > > commandline. The arrow keys don't work, ^C either does nothing (on the > first > > run of less) or interrupts the parent program, etc. > > > > I believe my mistake is that I am not correctly putting less into the > > foreground. I also suspect that I'm not correctly moving my go program > back > > into the foreground each time I kill the child less process. I'm > wondering > > if anyone knows the magical incantation that is required to make this > work > > properly. My current code is here (with the compiler replaced by a random > > number generator, since it is proprietary to the company I work for). I > have > > marked with TODOs the things I think are not working correctly. > > > > https://play.golang.org/p/Xv0y-Ln7aC > > > > Any ideas what I'm doing wrong here? > > Your program seems to work for me, so I guess I misunderstand what the > problem is. > > I ran `go build foo.go; ./foo`. It prints a series of random numbers > from 0 to 99, fed into less. When it prints a number 95 to 99, it > restarts less. When it prints enough numbers to fill my terminal, I > see the `less` prompt (a colon). I can use arrows, space, etc. > Eventually that instance of less is killed and a new one starts. > Hitting ^C just causes `less` to beep. Hitting `q` causes less and > the main program to exit. > > What do you see? (Note that you shouldn't use `go run` for a program > like this.) > Huh. It looks like it is working. The bug here is in my understanding of less. I thought that I could interrupt and get a prompt when I was looking at the unfinished part of a file. But it seems that doesn't work. So I probably need to provide an EOF once I'm sure there will be no more output, so the user can quit out from less if the build log is less than a full page long. There was also the issue of being able to interrupt the whole program with ^C during the second less and after. I believe that this was being caused by a race between starting the second less exec.Cmd and the TIOCSPGRP ioctl call at the end of the first one. The ioctl was stealing the foreground from the running less program, because it ran after the command started. Remove that call seems to fix the problem. Thanks so much for your help! -- James -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
