Julia EvansNov 24, 2024

every so often I get confused because I'm writing a zine about the terminal and didn't I already write 4 zines about the terminal???

but I've never written about what the UI “rules” you need to know to use the terminal interactively are, only:

- notes on core Unix concepts — file descriptors, signals, etc (Bite Size Linux)
- shell scripting (Bite Size Bash)
- cheat sheets for sed/grep/xargs/etc (Bite Size Command Line)
- cheat sheets for command line networking tools (Bite Size Networking)

Show threadJulia EvansNov 25, 2024

I haven't totally sold myself yet on this "what are the secret rules of the terminal?” framing but it feels like a reasonable way to talk about how, even though “the terminal” is a lot of separate things working together, it "feels" like a cohesive environment that has a lot of rules that you can generally expect to be true.

Some of those rules are Unchangeable Facts and some of them are just Vague Social Rules but understanding the vague social rules is just as important as knowing The Facts.

Show threadJulia EvansNov 25, 2024

an example of a "social rule" in the terminal is that if you have a noninteractive program, you can generally expect that `Ctrl-C` will stop it, programs can do whatever they want but it would just be kind of rude for a noninteractive program to not respect `Ctrl-C`

(there are different and more complicated social expectations around how to quit interactive programs)

Show threadJulia EvansNov 25, 2024

another example of a "social rule" is that at an interactive prompt you should expect `Ctrl-W` to delete the last word, this is weird because depending on the _kind_ of program, the exact mechanism for how `Ctrl-W` will delete the last word might change, but I think it would be generally considered rude if a program with an interactive prompt treated `Ctrl-W` in a different way

(text editors are an exception though and generally are allowed to handle text editing however they please)

Show threadJulia Evans

another social rule is that if a program is writing its stdout to a file or pipe, it's expected to turn off colour codes so that users don't end up looking at output like this:

ESC[1;33massets.jsESC[0m

(as far as I know there is almost nothing enforcing this behaviour except that users will be unhappy if you don't do it)

Nov 25, 2024 at 12:17amWeb
Show threadJulia EvansNov 25, 2024
another funny example of a "social rule" in the terminal is that it's not actually considered THAT rude for a program to not support arrow keys, like if the program only takes very limited interactive input (like just `y`/`n` or entering a number), then it's normal for the arrow keys to not work. Git is an example of this.
Show threadJulia EvansNov 25, 2024

i forgot to put “please don’t explain how terminal keybindings work to me” on this thread and i’m regretting it, anyway, please don’t, i wrote 4000 words about it if anyone wants a deep dive
https://jvns.ca/blog/2024/10/31/ascii-control-characters/

https://jvns.ca/blog/2024/07/08/readline/

ASCII control characters in my terminal

ASCII control characters in my terminal

Julia Evans
Show threadzellynNov 25, 2024
@b0rk Now I feel slightly guilty for explaining how `dup` works on that `stderr` redirection question… Sorry! (But hopefully I at least also validated the “try the wrong way, then the other one” as a viable alternate methodology 😂)
Show threadJulia EvansNov 25, 2024
@zellyn nah i always appreciate when people share their relationship to the fact (like “knowing this does not help me”), i know about dup but i don’t know how you relate to it :)
Show threadLucas GarronNov 26, 2024
@b0rk oh yeah, I’ve been disentangling so many of these in my head recently! Are you interested in more examples?
Show threadApril KingNov 27, 2024
@b0rk you might enjoy playing around with misbehaving.site, which has a bunch of URLs you can curl and which, depending on the implementation, can do all sorts of things (like minimize your terminal)
Show threadjn (big endian energy)Nov 25, 2024
@b0rk speaking of y/n prompts -- another pattern (or rule): if one of the options is stated in upper case, it should work as a default when pressing only the enter key
Show thread𝚗𝚎𝚘 𝚙𝚘𝚜𝚝 𝚖𝚘𝚍𝚎𝚛𝚗Nov 25, 2024
@jn
It took me a while to realize this implied a default instead of the necessity to type the letter in uppercase.
@b0rk
Show threadrsalzNov 25, 2024
@b0rk I don't know if it is a social rule, but rather common behavior enforced by the TTY driver that the terminal program uses. Or, rather, that the kernel runs whenever somebody reads from a terminal.
Show threadSamuel HierholzerNov 25, 2024
@rsalz @b0rk nope, the tty doesn't do anything with such escape sequences. The following stackexchange explains it quite well: https://unix.stackexchange.com/a/103764
Is there any reason why I get ^[[A when I press up arrow at the console login screen?

Whenever I'm at the console login, I press up arrow intentionally to see the previously typed commands. But I see this ^[[A. But when I press Ctrl Alt Print Screen Scroll Lock Pause Break Page Up ...

Unix & Linux Stack Exchange
Show threadrsalzNov 25, 2024
@sam @b0rk it does some of the things like ctrlC ctrlW delete etc
Show threadJulia EvansNov 25, 2024
@rsalz @sam can you leave me out of this conversation thanks
Show threadSamuel HierholzerNov 25, 2024
@rsalz Ok yeah I get it. And the kernel eats ctrl+alt+delete/shift+alt+FX/...
Show threadUrix TuringNov 25, 2024
@b0rk I thought of arguments having the short (ls -l) or long (ls --help) forms as a rule. But then there are the single-dash long forms (find . -type d), or the insane things like iproute(8), with -a/-all but also -br/-brief 😩
Show threadUrix TuringNov 25, 2024
@b0rk in addition to that, when the arguments have values the rule I think should be -lvalue and --long=value... But again, many exceptions to this rule
Show threadwakejagrNov 25, 2024

@b0rk

I think that each time I write a script, I have to decide all over again whether to accept a single keystroke or to accept a whole line of input.

AFAIK, there's no consensus on that.

Show threadThom SlatteryNov 27, 2024
@b0rk Love coming across threads of yours like this - they always make me stop and think. Like every time I hit ctrl-c and a command just quits I'm honestly a little surprised.
Show threadJoão S. O. BuenoNov 25, 2024
@b0rk that reminds ne that filtering these out shoiluld be an obvious capability of my terminedia project . (I still have no parser dor these ANSI codes)
Show threadEric EvansNov 25, 2024
@b0rk as an aside: my life was forever changed when I learned of less -R (raw), which lets you see saved output like that with colors. It doesn't help if you'd hoped to parse it ofc, but if you're reading it's nice not to have to try filtering those codes out with your eyeballs. 😃
Show threadBenjamin BraatzNov 25, 2024
@jericevans @b0rk I actually *like* to have coloured output also in `less`. So, I always have to find out what the option for “always with colour” is to give it to `less -R`.
Show threadmhoyeNov 25, 2024
@b0rk I really wish we could have structured data across pipes just so we could get highlighting back at the end of pipe-based tool chaining. Lumin is nice enough, but thin gruel in comparison.
Show threadChris PetrilliNov 25, 2024
@mhoye @b0rk this is one of the few things I really like about Powershell.
Show threadItamar Turner-TrauringNov 25, 2024
@petrillic @mhoye @b0rk nushell also does structured data, and is cross-platform
Show threadChris PetrilliNov 25, 2024
@itamarst @mhoye @b0rk oooo will check it out. I hate the general syntax of Powershell but the structured data aspect is a huge win.
Show threadmhoyeNov 25, 2024

@petrillic @itamarst @b0rk

I’m convinced that if powershell had been born anywhere but Microsoft it would have replaced bash entirely by now. Even structured data is thin gruel compared to pipelines passing structures objects.

Show threadjlongmanNov 25, 2024

@itamarst @petrillic @mhoye @b0rk

https://www.nushell.sh to save someone else some clicks. I’m definitely going to take a look at this.

I’m not sure if I found the right lumin? https://lumin.readthedocs.io/en/stable/

Nushell

A new type of shell.

Show threadDion WilliamsNov 25, 2024
@b0rk And it can be annoying when some apps handle this differently. For example, I think most utilities will check both isatty() and TERM != dumb to enable colouring by default. However, it seems like PowerShell only checks the latter, so it'll emit ANSI codes even when stdout is not a TTY.
Show threadTroubleNov 25, 2024

@b0rk it's not a social role, it's necessary to not break pipes. For example

echo this is the way | grep the | grep 'the way'

If the middle grep outputs ansi codes to colorize "the" to make it stand out, the last grep will not match and therefore output nothing.

Show threadCassandrichNov 25, 2024
@b0rk The old social rule I observe is that you never output color or other terminal escapes in straight output (not bidirectional terminal ui) regardless of whether output us a tty or not unless explicitly asked to, and I am angry every time some program violates that and I have to stop what I'm doing and spend 30 yak-shaving minutes researching how to get it to stop.
Show threadDan QNov 25, 2024
@b0rk Every time I notice that a program correctly follows the "social rule" of un-colorising it's stdout hen it's writing to a pipe, I briefly wonder: how? How does it know where it's stdout is going? Some day I'll learn how to do that in my programs.
Show threadThe0x539Nov 25, 2024
@dan I believe the general mechanism is isatty(3). I sometimes wish there were a way (an easy way?) to spoof this, because sometimes I want to redirect a program's tty-flavored output but cannot find a `--color always` equivalent flag.
Show threadDan QNov 25, 2024

@The0x539 Interesting. Don't know anything about it (yet!).

Can you spoof if by eg just piping to `cat`, or to `tee /dev/null` or something?

Show threadJulia EvansNov 25, 2024
@The0x539 @dan you can use “unbuffer program” to make its stdout a tty even if you redirect the output
Show threadI ForgetNov 25, 2024

@dan In unix and c it's the isatty() function. Usually you'd call that on stdout.

https://man.archlinux.org/man/isatty.3.en

Most other platforms and languages probably have something similar. For instance, when I duckduckgo "python isatty", "rust isatty", "golang isatty", "java isatty", or "js isatty", I find an example within the first couple hits.

Hope that helps!

isatty(3) — Arch manual pages

Show threaddokNov 25, 2024
@dan using istty on stdout file descriptor (1)