dye

• About
• Usage
• Development

Demo

About

dye is a portable and respectful library for adding color and emphasis to the output of shell scripts.

It's portable because

• it works on many Unix systems, including macOS, Linux, and OpenBSD;

• it is written to the POSIX shell standard, so it works in many shells that are POSIX-compatible, such as ash and Dash, Bash, ksh, and Zsh;

• it uses tput(1) instead of hard-wired ANSI sequences, so it will work wherever the appropriate terminal capabilities are available, and gracefully degrade where they are not; and

• it additionally degrades gracefully if tput(1) is not available (e.g. in a Docker alpine image where ncurses is not installed).

It's respectful because:

• it will disable if "NO_COLOR" is set;

• it will enable if "CLICOLOR" is set, but only if stdout is a tty;

• it will unconditionally enable (e.g. if stdout is not a tty) if "CLICOLOR_FORCE" is set;

• it allows script developers to choose to default to color off unless the user has opted in with environment variables; and

• it is written to only put functions and environment variables prefixed with "dye" or "DYE" into the shell's global namespace, and carefully avoids clobbering any existing shell variables during operation.

dye does call tput(1) for every terminal sequence it needs to output, so it's not screamingly fast. However, in practice, it's more than fast enough for the job I need it for: making the output of shell scripts colorful to make them easier to read and scan. If you're working with lots of color (for example, creating ANSI art), it's probably best to stick to a solution that caches ANSI sequences and forgo the portability.

I wrote dye to replace my previous project, portable-color. portable-color was fine, but would load lots of functions into the shell's global namespace. dye has a better API, with more capabilities and conveniences.

Usage

Embedding

You can use dye in your script by copying the contents of dye.sh above the place you will use it.

This the method I recommend. Shell scripts that I write are generally made to be self-contained, and embedding makes them very easy to download and use.

A couple notes on this strategy:

• If you end up changing dye's code, consider changing the names of the dye functions and variables that end up in the shell's global namespace, to avoid conflicts with the standard dye code that may be depended on elsewhere—particularly if you're removing functionality you do not use.

• If you distribute your script with dye's code inline, you must include a copy of the license in some way with your script. This specifically so others understand their rights in regard to the use of this software.

Sourcing

If you have dye.sh available on your PATH (executable bit not necessary), you can load it very simply:

. dye.sh || exit 1

If you include a copy alongside your script, you can also load it from a specific directory:

. ./dye.sh || exit 1

Initialization

dye must be initialized once before use, or no text changes will happen when you use the color or emphasis routines:

dye setup

"setup" is where dye will check things like whether stdout is a tty, whether environment variables like "NO_COLOR" and "CLICOLOR" are set, and make a decision whether or not to set the variable "DYE_COLORS" to the number of available colors, which the other routines will use.

An alternate mode for "setup" will not enable color by default, but will enable it if the user has "CLICOLOR" set:

dye setup default-off

Wrapping text

For simple color and emphasis, using dye to wrap quoted text is the most convenient method.

echo "$(dye green "It's not easy being... well, you know.")"

echo "So $(dye bold "bold"), it's not recommended for human consumption\!"

Quoting text is also not strictly necessary, but can result in the need to use many more escapes (just like it would if using "echo" straight up). It also means whitespace gets collapsed, so beware!

echo Quotes\? Quotes\? $(dye italic We don\'t need no stinking quotes\!)

Resets

When wrapping text, one key caveat applies: all colors and several emphases do not have a matching ending terminal sequence—they can only be turned off by sending an "sgr0" terminal capability to reset all color and emphasis.

dye will send this reset sequence at the end of wrapped text for colors and select emphases, so it's best not to stack wrappers. It gets unreadable really fast, anyway, so it's better to use manual control.

Manual control

More complex markup is easier to manage with manual control:

echo "$(dye cyan)$(dye bold)Cyan$(dye reset), $(dye magenta)$(dye bold
    )magenta$(dye reset), and $(dye bold)white$(dye reset
    ) ought to be enough for anybody."

Using lots of manual control can make lines pretty long, but as you can see, you can also leverage the fact that line breaks are valid inside command substitution to break them up.

Colors

Many colors are available for use, subject to terminal support.

There's the basic ANSI color set:

• black (or 0)
• red (or 1)
• green (or 2)
• yellow (or 3)
• blue (or 4)
• magenta (or 5)
• cyan (or 6)
• white (or 7, or brightgray)
• gray (or 8)
• brightred (or 9)
• brightgreen (or 10)
• brightyellow (or 11)
• brightblue (or 12)
• brightmagenta (or 13)
• brightcyan (or 14)
• brightwhite (or 15)

"dye yellow" will set the foreground color to yellow, for example. There are also "fg" and "bg" commands that will explicitly set the foreground or background color, respectively:

echo "$(dye bg blue)$(dye fg yellow)In Ann Arbor, everything is this color.$(dye reset)"

High colors

Some terminal definitions, like "ansi" and "xterm", don't recognize colors higher than 7. If "DYE_COLORS" is 8, indicating this scenario, dye will synthesize "bright" colors by turning on "bold" and setting the non-bright equivalent.

Note that this also means that "bold" may be turned on unexpectedly if you're using "bright" colors—so keep this situation in mind:

• If you're nesting wrapped text, make sure that nested text deals with the fact that "bold" might be on if you're using a "bright" color.

• If you're using manual control, be sure to reset at the appropriate time if the possiblity that "bold" might be on.

You can test to see how your code is working by setting TERM to "ansi" or "xterm" on many systems.

Emphases

Several emphases are available as well.

Resettable emphases

The first group, like colors, must be reset to turn them off:

• dim (makes things darker)
• bold
• reverse (see also "standout" below)

They can be used just like colors, and wrapping text with them will automatically send a reset at the end.

Endable emphases

The second group have "end" terminal sequences that can turn them off explicitly, with all other settings remaining in play:

• italic (or i)
• standout (or so, often displayed as reversed foreground and background)
• underline (or ul, or u)

When using one of these, you don't have to re-enable other modes:

echo "$(dye magenta)Mary $(dye italic "had") a little lamb.$(dye reset)"
echo "$(dye magenta)Mary had a $(dye italic "little") lamb.$(dye reset)"

For manual control, the "end" command can be used for these:

echo "Visit $(dye ul)https://mattiebee.dev/dye$(dye end ul) to get the code."

To match "end", "begin" is also available (and works with all emphases). It behaves the same way as just using the emphasis, e.g. "dye begin italic" is equivalent to "dye italic".

Development

Testing

Unit tests are exhaustively written in shellspec. The specs script will look for shells on your system that are expected to be compatible, and run the suite for each, stopping on the first failures.

coverage pairs shellspec with kcov in Docker to gather coverage while running against Bash. (I'm using Docker here because I can't get shellspec with kcov to work on macOS.) 100% is impossible to reach due to kcov thinking some syntax isn't covered. But all meaningful lines of dye.sh are covered.

Standards

Code should all be written to the POSIX shell spec. Deviations are probably bugs. 🐜

This is particularly important because dye should run everywhere it can, including in very limited systems. If it starts getting loaded up with Bashisms, it won't work in some places.

Notes

tput

During the development of dye, I did explore things like caching the output of tput(1) so it didn't have to be invoked quite so much.

The added complexity was really not worth it, since tput(1) is still fast enough (i.e. not at all noticeably slow) for most purposes where a shell script is doing work for at least a small amount of time. The cache would also need to be filled, and most scripts just don't switch colors enough to make it worthwhile.

The sequences dye generally uses are simple and unconcerned with this, but there are also interesting details with certain terminal control sequences on certain systems that tput(1) can handle if invoked directly, such as embedded delays. So, the practice also encourages maximum compatibility.