Safe terminal escape codes

A long time ago when the Unix greybeards were slightly less grey beards everyone was using hardware terminals to talk to some mainframe. Those terminals had wildly different feature sets and ways to implement them, which you needed to know about if you wanted your program to run on more than one type of terminal. Hence systems like terminfo and termcap.

The TeleVideo 955 used \x1b[=5l for bold text, and the IBM 3161 used \x1b4H. Both were introduced in 1985. The TeleVideo 950 from 1980 didn’t support bold text at all.

Today everyone is using software terminal emulators, and they all just implement ANSI escape codes for the common stuff. No one is sending \x1b[=5l or \x1b4H.

Do you still need terminfo? It depends. If you just want to style some text and maybe do some basic cursor operations: probably not. If you want to use more advanced operations or read key input: probably yes. If you want maximum compatibility (there’s probably someone using a hardware Wyse terminal, or SunOS 4 with CDE): absolutely.

Here is a list of terminal escape sequences that should always work on any vaguely modern terminal, where “modern” means “since the mid-90s or so”.

This was generated by looking at every terminfo file I could find with my termfo tool (specifically, termfo find-cap) and occasionally testing some things to verify it works. I don’t care what some spec says; I care about what works.

The escape character is always omitted; so [0m is \x1b[0m.

Graphics

These can be combined in a single sequence by joining with a ;. For example \x1b[1;4m for underlined bold text. These can also be combined with colours; for example \x1b[1;38;2;0;255;0;41m to set bold, foreground colour with true colour, and background colour with 16 colour.

Just using \x1b[1m\x1b[4m also works.

Colours are set with setab / set_a_background and setaf / set_a_foreground; the format depends on which colour scheme you want to use.

16-colours

Pretty much everything supports 16 colours, unless explicitly disabled by the user. The exact shade is determined by the terminal.

Escapes as «regular» «bright»:

256-colours

Choose a colour from a pre-defined table of 256 colours. This is supported on almost all current terminal emulators, unless explicitly disabled by the user.

Where «C» is a number from 0 to 255:

[38;5;«C»m   Foreground
[48;5;«C»m   Background

True colours

Use “true” RGB colours; this is supported on almost all current terminal emulators, unless explicitly disabled by the user.

Where «R», «G», «B» are the red, green and blue values as decimal, 0 to 255:

[38;2;«R»;«R»;«B»m   Foreground
[48;2;«R»;«G»;«B»m   Background

Cursor movement

The «N» can be omitted in the above, in which case it will default to 1. For cup the «R» and/or «C» can be omitted, and will default to 1.

Inserting and deleting text

The «N» can be omitted in the above, in which case it will default to 1.

Misc

Keys

Key input handling is kind of a mess, and this is where I really recommend using a terminfo library if at all possible. This also avoids the whole backspace/delete key confusion (less of an issue today than it used to be, but still exists).