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I've been programming for 20 years and apparently still don't understand what my terminal is doing. Recently I asked Claude Code to generate a small shell script. It came back full of escape codes and I just stared at it like a caveman looking at a smartphone. This article finally explains what's been happening right under my nose.
No mention whatsoever of the $TERM environment variable. sigh
Outputting raw escape codes and hope that they work is not how you do it. This is not how any reasonable library (or bash, or git, etc.) does it. These programs and libraries start with the $TERM environment variable to find out what terminal the user is using, and then use something like termcap(5) or terminfo(5) to look up what capabilities that specific terminal has, and what actual escape codes to output to get that effect. In reality, though, most regular programs delegate all this to a library, like ncurses.
(And also make sure not to output any terminal codes at all if the standard output is not a terminal, as in isatty(3) or tty(1).)
This way, you can check for and use modern cool stuff like sixels, but not use them if some user is using something older like XTerm or the Windows Console.
Indeed, but also termcap is a tire fire. I like the way Ghostty deals with it: https://ghostty.org/docs/help/terminfo
Even then it still leaves a lot to be desired. I'm not sure I can consider any of this to be truly reasonable.
> No mention whatsoever of the $TERM environment variable. sigh
I have mixed feelings about this... Sometimes I feel young and reckless and want to just output whatever I need without checking $TERM. In practice, all modern terminal emulators are essentially xterm-256color compatible. If something breaks, the worse you get is some funny characters. Is that such a big deal? Much better than propagate the silly termcap/terminfo complexity.
By the way, xterm supports sixels since forever.
If you're going to do this also provide a way to disable it so parsers don't trip up on its escape-coded output.
Also, disable the formatting if stdout is not a terminal. That way, your colors and cursor movements won't be visible when piping to another program, and your tool will be usable in apps that don't understand the CSI and chars that follow. Use a command-line switch with more than two states, e.g., `ls` (and probably other GNU tools) has `--color=always|auto|never` which covers most use cases.
Also not mentioned in the article: there are a few syntaxes available for specifying things in control sequences, like
\x1b[38;2;{r};{g};{b}m