Weekly - issue 45

2023-11-19

Using Colors in Terminal Output

ANSI escape sequences is a standard to control cursor location, color, font styling, and other options on terminal emulators.

The sequences are grouped by their sequence type. CSI (Control Sequence Introducer) is one of the groups, their sequence starting with ESC [. SGR (Select Graphic Rendition) is a part of CSI, it sets display attributes.

The form of SGR:

ESC [ n m

# In terminal, we can write
\e[nm
# or
\x1b[nm

ESC is a character in the ASCII table.

n consists of one or more decimal digits, separated by ;.

The sequence ends with m.

Sequence	Description
ESC [ 30…37 m	Set ANSI text color
ESC [ 38 ; 5 ; n m	Set text color, 256-color, n is color index from 0 to 255
ESC [ 38 ; 2 ; r ; g ; b m	Set text color, 24-bit true color, r, g, b are from 0 to 255
ESC [ 39 m	Reset text color to default
ESC [ 40…47 m	Set ANSI background color
ESC [ 48 ; 5 ; n m	Set background color, 256-color, n is color index from 0 to 255
ESC [ 48 ; 2 ; r ; g ; b m	Set background color, 24-bit true color, r, g, b are from 0 to 255
ESC [ 49 m	Reset background color to default
ESC [ 90…97 m	Set bright ANSI text color
ESC [ 100…107 m	Set bright ANSI background color
ESC [ 1 m	Bold
ESC [ 0 m	Reset

ANSI colors:

Text Color	Background Color	Color Name
30	40	black
31	41	red
32	42	green
33	43	yellow
34	44	blue
35	45	magenta
36	46	cyan
37	47	white

# red A
echo '\e[31mA'

# white A, red background
echo '\e[37;41mA'

# bright and bold A, red background
echo '\e[1;97;41mA'

# red A, green B
echo '\e[31mA\e[0B\e[32mB'

To print 256 text and background colors:

#!/usr/bin/env python3

# text colors
for i in range(0, 16):
    for j in range(0, 16):
        code = str(i * 16 + j)
        print(f"\x1b[38;5;{code}m{code.ljust(4)}", end=' ')
    print("\x1b[0m")

# background colors
for i in range(0, 16):
    for j in range(0, 16):
        code = str(i * 16 + j)
        print(f"\x1b[48;5;{code}m{code.ljust(4)}", end=' ')
    print("\x1b[0m")

Discovering Recently Installed Commands In Zsh

When using Zsh (with Oh My ZSH), the newly installed commands will not be automatically completed without opening new terminal tab or window. We can run the command to fix it:

rehash
# or
hash -rf