Trippy colors
You’ve probably notices that some commands can output colorful text in the terminal. Here is how to do it yourself.
Here is a teaser.
echo -e "\e[32mHello World\e[0m"
Background
It gets a bit technical.
The -e flag makes echo interpret backslash escapes.
With it we can type in \ followed by a character code to output
none-printable characters.
You see, terminals are based on the ASCII standard for encoding character. Each symbol shown on the screen needs to be encoded in binary somehow. ASCII is just a way to encode those.
ASCII table shows how characters are encoded.
Instead of writing long sequences like “00001010” for “a” it is common to use either decimal (0-255), hex (00-ff) or octal (000-377) to represent a byte. Btw ASCII only uses 7-bits, so the last bit have been used for various extensions including UTF-8.
The letter “a” has the character code 61 in hex or 141 in octal. It can be printed using a backslash sequence:
# hex
echo -e "\x61"
# octal
echo -e "\0141"
Not terrible exiting, but it illustrates the idea.
To do something a bit more fun, we can try to ring the terminal bell. It will either make a sound or give a visual clue depending on your terminal emulator.
echo -e "\x07"
If we echo the character code for escape, then we can use a special sequence to control how the terminal prints characters.
echo -e "\033[1mHello World"
Where “\033” is escape and “[1m” is a control code to make text bold.
Because “\033” is annoying to remember, there is also the shortcut “\e”.
Fun stuff
Note: support depends on your terminal.
To set foreground color to red:
echo -e "\e[31mRed"
To set background color to red:
echo -e "\e[41mRed"
Here is a table of the standard colors.
| Color | Foreground | Background |
|---|---|---|
| Black | 30 | 40 |
| Red | 31 | 41 |
| Green | 32 | 42 |
| Yellow | 33 | 33 |
| Blue | 34 | 44 |
| Magenta | 35 | 45 |
| Cyan | 36 | 46 |
| Gray | 37 | 47 |
Depending on your terminal, it might also be possible to go full RGB mode.
echo -e "\e[38;2;255;192;203mPink"
RGB color (255, 192, 203) for pink.
We can also change the text in various other ways. Here are some examples:
echo -e "\e[1m Bold"
echo -e "\e[3m Italic"
echo -e "\e[4m Underline"
echo -e "\e[5m Slow blink"
echo -e "\e[6m Fast blink"
Last, use “\e[0m” to reset.
echo -e "\e[32mColor \e[0mReset"