How to change text color in a Linux terminal
source link: https://www.codeproject.com/Articles/5329247/How-to-change-text-color-in-a-Linux-terminal
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Introduction
The default text output to a terminal is monochromatic and doesn't provide a simple method to provide context. For instance you may want an error to appear in red, success in green, or important info to be output in bold.
Adding color to your terminal output is straightforward and involves outputting the correct control characters before your text.
Terminal colors
To output colored text you need to printf or echo -e (the -e to ensure control characters are interpeted) the control characters for the required color, then output your text, and then (to be tidy) reset the output back to defaults. The following table lists the codes
Color Foreground Background Default \033[39m \033[49m Black \033[30m \033[40m Dark red \033[31m \033[41m Dark green \033[32m \033[42m Dark yellow (Orange-ish) \033[33m \033[43m Dark blue \033[34m \033[44m Dark magenta \033[35m \033[45m Dark cyan \033[36m \033[46m Light gray \033[37m \033[47m Dark gray \033[90m \033[100m Red \033[91m \033[101m Green \033[92m \033[101m Orange \033[93m \033[103m Blue \033[94m \033[104m Magenta \033[95m \033[105m Cyan \033[96m \033[106m White \033[97m \033[107m
and the reset code is \033[0m
The format of the string for foreground color is:
"\033[" + "<0 or 1, meaning normal or bold>;" + "<color code> + "m"
and for background:
"\033[" + "<color code>" + "m"
These codes can be output together in order to change fore- and back-ground colors simultaneously.
Using the code
A simple example of red text
printf "\033[91mThis is red text\033[0m"
An example of red text on a white background
printf "\033[91m\033[107mThis is red text on a white background\033[0m"
This is a little cumbersome so I've created some simple subroutines that provide the means to output text in a more civilised manner
Helper functions
The following helper functions allow you to do stuff like
WriteLine "This is red text" "Red" WriteLine "This is red text on a white background" "Red" "White"
Much easier.
useColor="true" # Set to false if you find your environment just doesn't handle colors well
# Returns a color code for the given foreground/background colors
# This code is echoed to the terminal before outputing text in
# order to generate a colored output.
#
# string foreground color name. Optional if no background provided.
# Defaults to "Default" which uses the system default
# string background color name. Optional. Defaults to $color_background
# which is set based on the current terminal background
# returns a string
function Color () {
local foreground=$1
local background=$2
if [ "$foreground" == "" ]; then foreground="Default"; fi
if [ "$background" == "" ]; then background="$color_background"; fi
local colorString='\033['
# Foreground Colours
case "$foreground" in
"Default") colorString='\033[0;39m';;
"Black" ) colorString='\033[0;30m';;
"DarkRed" ) colorString='\033[0;31m';;
"DarkGreen" ) colorString='\033[0;32m';;
"DarkYellow" ) colorString='\033[0;33m';;
"DarkBlue" ) colorString='\033[0;34m';;
"DarkMagenta" ) colorString='\033[0;35m';;
"DarkCyan" ) colorString='\033[0;36m';;
"Gray" ) colorString='\033[0;37m';;
"DarkGray" ) colorString='\033[1;90m';;
"Red" ) colorString='\033[1;91m';;
"Green" ) colorString='\033[1;92m';;
"Yellow" ) colorString='\033[1;93m';;
"Blue" ) colorString='\033[1;94m';;
"Magenta" ) colorString='\033[1;95m';;
"Cyan" ) colorString='\033[1;96m';;
"White" ) colorString='\033[1;97m';;
*) colorString='\033[0;39m';;
esac
# Background Colours
case "$background" in
"Default" ) colorString="${colorString}\033[49m";;
"Black" ) colorString="${colorString}\033[40m";;
"DarkRed" ) colorString="${colorString}\033[41m";;
"DarkGreen" ) colorString="${colorString}\033[42m";;
"DarkYellow" ) colorString="${colorString}\033[43m";;
"DarkBlue" ) colorString="${colorString}\033[44m";;
"DarkMagenta" ) colorString="${colorString}\033[45m";;
"DarkCyan" ) colorString="${colorString}\033[46m";;
"Gray" ) colorString="${colorString}\033[47m";;
"DarkGray" ) colorString="${colorString}\033[100m";;
"Red" ) colorString="${colorString}\033[101m";;
"Green" ) colorString="${colorString}\033[102m";;
"Yellow" ) colorString="${colorString}\033[103m";;
"Blue" ) colorString="${colorString}\033[104m";;
"Magenta" ) colorString="${colorString}\033[105m";;
"Cyan" ) colorString="${colorString}\033[106m";;
"White" ) colorString="${colorString}\033[107m";;
*) colorString="${colorString}\033[49m";;
esac
echo "${colorString}"
}
# Outputs a line, including linefeed, to the terminal using the given foreground / background
# colors
#
# string The text to output. Optional if no foreground provided. Default is just a line feed.
# string Foreground color name. Optional if no background provided. Defaults to "Default" which
# uses the system default
# string Background color name. Optional. Defaults to $color_background which is set based on the
# current terminal background
function WriteLine () {
local resetColor='\033[0m'
local str=$1
local forecolor=$2
local backcolor=$3
if [ "$str" == "" ]; then
printf "\n"
return;
fi
# Note the use of the format placeholder %s. This allows us to pass "--" as strings without error
if [ "$useColor" == "true" ]; then
local colorString=$(Color ${forecolor} ${backcolor})
printf "${colorString}%s${resetColor}\n" "${str}"
else
printf "%s\n" "${str}"
fi
}
# Outputs a line without a linefeed to the terminal using the given foreground / background colors
#
# string The text to output. Optional if no foreground provided. Default is just a line feed.
# string Foreground color name. Optional if no background provided. Defaults to "Default" which
# uses the system default
# string Background color name. Optional. Defaults to $color_background which is set based on the
# current terminal background
function Write () {
local resetColor="\033[0m"
local forecolor=$1
local backcolor=$2
local str=$3
if [ "$str" == "" ]; then
return;
fi
# Note the use of the format placeholder %s. This allows us to pass "--" as strings without error
if [ "$useColor" == "true" ]; then
local colorString=$(Color ${forecolor} ${backcolor})
printf "${colorString}%s${resetColor}" "${str}"
else
printf "%s" "$str"
fi
}
Handling Dark Mode and Light Mode
In many Linux and Unix distros the terminal is black background, white text. On macOS the default is white background with black text. There are ways and means to test and guess what's happening but ultimately you'll need to test on your system and decide what works for you.
What I do is assume that if we're on a mac then we can test directly, otherwise we assume white on black. I then also try to stick to default colors, and where I want a bit of colour I'll stick to some predefined colors I know will work well anywhere.
# Gets the terminal background color. It's a very naive guess
# returns an RGB triplet, values from 0 - 64K
function getBackground () {
if [[ $OSTYPE == 'darwin'* ]]; then
osascript -e \
'tell application "Terminal"
get background color of selected tab of window 1
end tell'
else
# See https://github.com/rocky/shell-term-background/blob/master/term-background.bash
# for a comprehensive way to test for background colour. For now we're just going to
# assume that non-macOS terminals have a black background.
echo "0,0,0" # we're making assumptions here
fi
}
# Determines whether or not the current terminal is in dark mode (dark background, light text)
# returns "true" if running in dark mode; false otherwise
function isDarkMode () {
local bgColor=$(getBackground)
IFS=','; colors=($bgColor); IFS=' ';
# Is the background more or less dark?
if [ ${colors[0]} -lt 20000 ] && [ ${colors[1]} -lt 20000 ] && [ ${colors[2]} -lt 20000 ]; then
echo "true"
else
echo "false"
fi
}
Once we have a rough idea of what we're dealing with I'll do:
darkmode=$(isDarkMode) # Setup some predefined colours. Note that we can't reliably determine the background # color of the terminal so we avoid specifically setting black or white for the foreground # or background. You can always just use "White" and "Black" if you specifically want # this combo, but test thoroughly if [ "$darkmode" == "true" ]; then color_primary="Blue" color_mute="Gray" color_info="Yellow" color_success="Green" color_warn="DarkYellow" color_error="Red" else color_primary="DarkBlue" color_mute="Gray" color_info="Magenta" color_success="DarkGreen" color_warn="DarkYellow" color_error="Red" fi
and to use these:
WriteLine "Predefined colors on default background" WriteLine WriteLine "Default colored text" "Default" WriteLine "Primary colored text" $color_primary WriteLine "Mute colored text" $color_mute WriteLine "Info colored text" $color_info WriteLine "Success colored text" $color_success WriteLine "Warning colored text" $color_warn WriteLine "Error colored text" $color_error WriteLine WriteLine "Default color on predefined background" WriteLine WriteLine "Default colored background" "Default" WriteLine "Primary colored background" "Default" $color_primary WriteLine "Mute colored background" "Default" $color_mute WriteLine "Info colored background" "Default" $color_info WriteLine "Success colored background" "Default" $color_success WriteLine "Warning colored background" "Default" $color_warn WriteLine "Error colored background" "Default" $color_error
On a classic Linux terminal
On a macOS terminal
Things are a bit murky so let's add one more function that will provide a contrasting foreground on whatever background we choose
# Returns the name of a color that will providing a contrasting foreground
# color for the given background color. This function assumes $darkmode has
# been set globally.
#
# string background color name.
# returns a string representing a contrasting foreground colour name
function ContrastForeground () {
local color=$1
if [ "$color" == "" ]; then color="Default"; fi
if [ "$darkmode" == "true" ]; then
case "$color" in
"Default" ) echo "White";;
"Black" ) echo "White";;
"DarkRed" ) echo "White";;
"DarkGreen" ) echo "White";;
"DarkYellow" ) echo "White";;
"DarkBlue" ) echo "White";;
"DarkMagenta" ) echo "White";;
"DarkCyan" ) echo "White";;
"Gray" ) echo "Black";;
"DarkGray" ) echo "White";;
"Red" ) echo "White";;
"Green" ) echo "White";;
"Yellow" ) echo "Black";;
"Blue" ) echo "White";;
"Magenta" ) echo "White";;
"Cyan" ) echo "Black";;
"White" ) echo "Black";;
*) echo "White";;
esac
else
case "$color" in
"Default" ) echo "Black";;
"Black" ) echo "White";;
"DarkRed" ) echo "White";;
"DarkGreen" ) echo "White";;
"DarkYellow" ) echo "White";;
"DarkBlue" ) echo "White";;
"DarkMagenta" ) echo "White";;
"DarkCyan" ) echo "White";;
"Gray" ) echo "Black";;
"DarkGray" ) echo "White";;
"Red" ) echo "White";;
"Green" ) echo "Black";;
"Yellow" ) echo "Black";;
"Blue" ) echo "White";;
"Magenta" ) echo "White";;
"Cyan" ) echo "Black";;
"White" ) echo "Black";;
*) echo "White";;
esac
fi
echo "${colorString}"
}
To use we simply do
WriteLine WriteLine "Default contrasting color on predefined background" WriteLine WriteLine "Primary colored background" $(ContrastForeground $color_primary) $color_primary WriteLine "Mute colored background" $(ContrastForeground $color_mute) $color_mute WriteLine "Info colored background" $(ContrastForeground $color_info) $color_info WriteLine "Success colored background" $(ContrastForeground $color_success) $color_success WriteLine "Warning colored background" $(ContrastForeground $color_warn) $color_warn WriteLine "Error colored background" $(ContrastForeground $color_error) $color_error
On a Linux terminal
on a macOS terminal
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