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0 pointsburke11y ago0 comments

I think it depends what sort of things you use it for. I often use it to switch on or off ANSI colourization, which doesn't really violate the principle of least surprise.

When used sparingly and thoughtfully, I've never personally had an issue with it.

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8 comments · 2 top-level

chriswarbo11y ago· 3 in thread

You may not have issue with the sort of things you use it for, but others might.

For example, I run shells in Emacs and have had to tweak loads of shell scripts written by colleagues to fix their poorly-implemented colourisation. It's useful to know when a test has failed; it's not so useful to have the whole terminal set to white text on a pale pink background.

One day I couldn't SSH into our servers from Emacs. It turned out somebody had edited .bashrc for the admin user to make the bash prompt blue. Emacs' TRAMP process was looking for a prompt ending in "$" or "#", not "$\[\033[0m\]", so it didn't realise the connections were successful.

There are two ways of handling this: we can blame the source of the bug (the person adding the colours incorrectly, or the assumption-loaded TRAMP regex), but there will always be more bugs in situations we'd never think of. Alternatively, we can avoid being 'too clever', and instead aim for consistency and least surprise.

gknoy11y ago

As much as I love Emacs, that sounds like it's a bug to assume that one's prompt will follow a convention (ends-in-$). The convention is useful and good, but it seems strange to blame someone for breaking your tool's expectations when they had made a valid prompt.

philh11y ago

Are you suggesting that colored prompts violate the rules of consistency and least surprise?

(Actually, if you are suggesting that, I'm not going to disagree. But I am going to say that if so, those rules don't apply in the case of colored prompts, because colored prompts are useful.)

chriswarbo11y ago

I suppose I'm suggesting that, aside from personal scripts, we shouldn't assume too much about who our users are and what they're trying to do. The principle of least power tells us to use the dumbest format that will work, eg. plain text.

Anything we add on top of that, eg. ANSI colour codes, will be useful to some but harmful to others. The tricky part is working out which of those categories the current user is in.

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dap11y ago· 3 in thread

Good point, and it makes me even more convinced that all rules of thumb have important exceptions. In fact, I've also used tools that use ANSI colorization, and disable that when not talking to a tty, and wished that they wouldn't because I was piping them to "less -R" :) (At least that's a graceful failure mode, and it's pretty clear what probably happened even if one doesn't exactly understand the details.)

burkeOP11y ago

I've always thought it would be nice to have a utility like cat that I could pipe commands to, which would trick them into thinking all their streams were attached to a tty, so you could do "uses_colours | ttycat | less -R".

I'm sure it's possible, but you'd have to acquire a new pty and decide what termios settings you want. It's a nontrivial hack, I think.

I'm actually kind of surprised it's not in moreutils[1].

[1]: https://joeyh.name/code/moreutils/

EDIT: Hmm, maybe it's not possible. I can't figure out exactly how to do it, anyway.

EDIT again: Apparently `script` does this on Linux: http://monosnap.com/image/Qlig4CHmQgV9pxvSmndVUgMTU88Adz

EDIT again: Expect's `unbuffer` also does it: http://expect.sourceforge.net/example/unbuffer.man.html#toc

JdeBP11y ago

> I've always thought it would be nice to have a utility like cat that I could pipe commands to, which would trick them into thinking all their streams were attached to a tty,

Daniel J. Bernstein wrote a "pty" package back around 1991 that did this. Version 4 of the package was published in 1992 to comp.sources.unix (volume 25 issues 127 to 135). It's still locatable on the World Wide Web.

Bernstein later updated this, around 1999, with a "ptyget" package that was more modular and that had the session management commands moved out of the toolset to elsewhere. The command from that package to do exactly what you describe is "ptybandage". There is also "ptyrun". Paul Jarc still publishes a fixed version of ptyget (that attempts to deal with the operating-system-specific pseudo-terminal device ioctls in the original) at http://code.dogmap.org./ptyget/ .

As a bonus feature for people who use source code, there are similar "ptybandage" and "ptyrun" scripts, for which you will need Laurent Bercot's execline tool (http://skarnet.org./software/execline/), in the source archive for the nosh package at http://homepage.ntlworld.com./jonathan.deboynepollard/Softwa... . These make use of the terminal-management tools in the nosh toolset.

With both of these, you should be able to run "ptybandage uses_colours_if_tty | less -R"

dnlrn11y ago

It’s not possible in the way you think, because the two programs don’t know about each other. All the pipe character does is put the stdout into the stdin of the other program.

So this feature must actually be present in the shell and maybe it is. I’m no expert but maybe zsh already offers something like this?

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