When writing shell scripts, I’d often resort to using hardcoded ANSI escape codes1 to format text, such as:

#!/usr/bin/env bash

BOLD="\033[1m"
UNBOLD="\033[22m"
FG_RED="\033[31m"
BG_YELLOW="\033[43m"
BG_BLUE="\033[44m"
RESET="\033[0m"

# Print a message in bold red text on a yellow background.
echo -e "${BOLD}${FG_RED}${BG_YELLOW}This is a warning message${RESET}"

# Print a message in white text on a blue background.
echo -e "${BG_BLUE}This is a debug message${RESET}"

This shell snippet above shows how to add text formatting and color to shell script output via ANSI escape codes. It defines a few variables that contain different escape codes for bold, unbold, foreground, and background colors. Then, we echo two log messages with different colors and formatting options.

The first message is printed in bold red text on a yellow background, while the second message is printed in white text on a blue background. To ensure that subsequent output is not affected by the previous formatting, the RESET variable is used to reset all color and formatting options back to their defaults after each message is printed. The -e option is used with echo to enable the interpretation of backslash escapes, which includes the ANSI escape codes.

While this works fairly well, every time I have to write a fancy shell script, I have to either look up the ANSI color codes, copy-paste from an existing script, or explain to an LLM what I need. Then chatGPT serendipitously recommended a shell tool called tput that makes this workflow quite a bit better. Underneath tput also uses ANSI escape codes to control various text formatting options but it doesn’t require you to hardcode these ugly escape codes.

Basic usage

The basic syntax of the tput command goes as follows:

tput <formatting_option>

Formatting options

Here are some commonly used tput formatting options:

  • setaf <color>: set the foreground (text) color to a specific color. For example, setaf 1 sets the color to red, while setaf 2 sets the color to green.
  • setab <color>: set the background color to a specific color.
  • bold: set the text to bold.
  • sgr0: reset all formatting options to their defaults.
  • smul: underline the text.

Example usage

#!/usr/bin/env bash

# Print text in red on a yellow background
tput setaf 1
tput setab 3
echo "Error: some error occurred"
tput sgr0

# Print bold text
tput bold
echo "This text is bold"
tput sgr0

# Print underlined text in blue
tput setaf 4
tput smul
echo "This text is underlined and blue"
tput sgr0

# Print text with a custom RGB color
tput setaf 38 # specify an RGB color using 8-bit mode
tput setaf 5 # specify a color index in 256-color mode
echo "This text is in a custom color"

# Print text with a background color gradient
tput setaf 0
for i in {0..7}; do
    tput setab $i
    echo "Background color $i"
done
tput sgr0

# Print blinking text
tput blink
echo "This text is blinking"
tput sgr0

Running the script will give you the following output:

tput color

This also hardcodes the color and formatting codes but it’s much easier than having to remember or search for the ANSI escape codes. Currently, I’m using a 256-bit macOS terminal and it supports fairly large sets of formatting options. You can run man tput to find out other features that are supported by your terminal. The following loop will print all the supported colors:

for i in {0..255}; do
    tput setab $i
    printf "  "
    tput sgr0
done

On my terminal, it prints this nice color palette:

tput color palette

  1. Escape codes ↩︎

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