Terminal codes (ANSI/VT100) introduction
https://wiki.bash-hackers.org/scripting/terminalcodes?
Terminal (control) codes are used to issue specific commands to your terminal. This can be related to switching colors or positioning the cursor, i.e. anything that can't be done by the application itself.
How it technically works
A terminal control code is a special sequence of characters that is printed (like any other text). If the terminal understands the code, it won't display the character-sequence, but will perform some action. You can print the codes with a simple echo
command.
Note: I see codes referenced as “Bash colors” sometimes (several “Bash tutorials” etc…): That's a completely incorrect definition.
The tput command
Because there's a large number of different terminal control languages, usually a system has an intermediate communication layer. The real codes are looked up in a database for the currently detected terminal type and you give standardized requests to an API or (from the shell) to a command.
One of these commands is tput
. Tput accepts a set of acronyms called capability names and any parameters, if appropriate, then looks up the correct escape sequences for the detected terminal in the terminfo
database and prints the correct codes (the terminal hopefully understands).
The codes
In this list I'll focus on ANSI/VT100 control codes for the most common actions - take it as quick reference. The documentation of your terminal or the terminfo
database is always the preferred source when something is unclear! Also the tput
acronyms are usually the ones dedicated for ANSI escapes!
I listed only the most relevant codes, of course, any ANSI terminal understands many more! But let's keep the discussion centered on common shell scripting
If I couldn't find a matching ANSI escape, you'll see a as the code. Feel free to mail me or fix it.
The ANSI codes always start with the ESC character. (ASCII 0x1B or octal 033) This isn't part of the list, but you should avoid using the ANSI codes directly - use the tput
command!
All codes that can be used with tput
can be found in terminfo(5). (on OpenBSD at least)
See OpenBSD's terminfo(5) under the Capabilities section. The cap-name is the code to use with tput. A description of each code is also provided.
General useful ASCII codes
The Ctrl-Key representation is simply associating the non-printable characters from ASCII code 1 with the printable (letter) characters from ASCII code 65 (“A”). ASCII code 1 would be ^A
(Ctrl-A), while ASCII code 7 (BEL) would be ^G
(Ctrl-G). This is a common representation (and input method) and historically comes from one of the VT series of terminals.
Name | decimal | octal | hex | C-escape | Ctrl-Key | Description |
---|---|---|---|---|---|---|
BEL | 7 | 007 | 0x07 | \a | ^G | Terminal bell |
BS | 8 | 010 | 0x08 | \b | ^H | Backspace |
HT | 9 | 011 | 0x09 | \t | ^I | Horizontal TAB |
LF | 10 | 012 | 0x0A | \n | ^J | Linefeed (newline) |
VT | 11 | 013 | 0x0B | \v | ^K | Vertical TAB |
FF | 12 | 014 | 0x0C | \f | ^L | Formfeed (also: New page NP ) |
CR | 13 | 015 | 0x0D | \r | ^M | Carriage return |
ESC | 27 | 033 | 0x1B | <none> | ^[ | Escape character |
DEL | 127 | 177 | 0x7F | <none> | <none> | Delete character |
Cursor handling
ANSI | terminfo equivalent | Description |
---|---|---|
[ <X> ; <Y> H [ <X> ; <Y> f | cup <X> <Y> | Home-positioning to X and Y coordinatesit seems that ANSI uses 1-1 as home while tput uses 0-0 |
[ H | home | Move cursor to home position (0-0) |
7 | sc | Save current cursor position |
8 | rc | Restore saved cursor position |
most likely a normal code like \b | cub1 | move left one space (backspace) |
VT100 [ ? 25 l | civis | make cursor invisible |
VT100 [ ? 25 h | cvvis | make cursor visible |
Erasing text
ANSI | terminfo equivalent | Description |
---|---|---|
[ K [ 0 K | el | Clear line from current cursor position to end of line |
[ 1 K | el1 | Clear line from beginning to current cursor position |
[ 2 K | el2 | Clear whole line (cursor position unchanged) |
General text attributes
ANSI | terminfo equivalent | Description |
---|---|---|
[ 0 m | sgr0 | Reset all attributes |
[ 1 m | bold | Set “bright” attribute |
[ 2 m | dim | Set “dim” attribute |
[ 3 m | smso | Set “standout” attribute |
[ 4 m | set smul unset rmul | Set “underscore” (underlined text) attribute |
[ 5 m | blink | Set “blink” attribute |
[ 7 m | rev | Set “reverse” attribute |
[ 8 m | invis | Set “hidden” attribute |
Foreground coloring
ANSI | terminfo equivalent | Description |
---|---|---|
[ 3 0 m | setaf 0 | Set foreground to color #0 - black |
[ 3 1 m | setaf 1 | Set foreground to color #1 - red |
[ 3 2 m | setaf 2 | Set foreground to color #2 - green |
[ 3 3 m | setaf 3 | Set foreground to color #3 - yellow |
[ 3 4 m | setaf 4 | Set foreground to color #4 - blue |
[ 3 5 m | setaf 5 | Set foreground to color #5 - magenta |
[ 3 6 m | setaf 6 | Set foreground to color #6 - cyan |
[ 3 7 m | setaf 7 | Set foreground to color #7 - white |
[ 3 9 m | setaf 9 | Set default color as foreground color |
Background coloring
ANSI | terminfo equivalent | Description |
---|---|---|
[ 4 0 m | setab 0 | Set background to color #0 - black |
[ 4 1 m | setab 1 | Set background to color #1 - red |
[ 4 2 m | setab 2 | Set background to color #2 - green |
[ 4 3 m | setab 3 | Set background to color #3 - yellow |
[ 4 4 m | setab 4 | Set background to color #4 - blue |
[ 4 5 m | setab 5 | Set background to color #5 - magenta |
[ 4 6 m | setab 6 | Set background to color #6 - cyan |
[ 4 7 m | setab 7 | Set background to color #7 - white |
[ 4 9 m | setab 9 | Set default color as background color |
Misc codes
Save/restore screen
Used capabilities: smcup
, rmcup
You've undoubtedly already encountered programs that restore the terminal contents after they do their work (like vim
). This can be done by the following commands:
# save, clear screen tput smcup clear # example "application" follows... read -n1 -p "Press any key to continue..." # example "application" ends here # restore tput rmcup
These features require that certain capabilities exist in your termcap/terminfo. While xterm
and most of its clones (rxvt
, urxvt
, etc) will support the instructions, your operating system may not include references to them in its default xterm profile. (FreeBSD, in particular, falls into this category.) If `tput smcup` appears to do nothing for you, and you don't want to modify your system termcap/terminfo data, and you KNOW that you are using a compatible xterm application, the following may work for you:
echo -e '\033[?47h' # save screen echo -e '\033[?47l' # restore screen
Certain software uses these codes (via their termcap capabilities) as well. You may have seen the screen save/restore in less
, vim
, top
, screen
and others. Some of these applications may also provide configuration options to *disable* this behaviour. For example, less
has a -X
option for this, which can also be set in an environment variable:
export LESS=X less /path/to/file
Similarly, vim
can be configured not to “restore” the screen by adding the following to your ~/.vimrc
:
set t_ti= t_te=
Additional colors
Some terminal emulators support additional colors. The most common extension used by xterm-compatible terminals supports 256 colors. These can be generated by tput
with seta{f,b} [0-255]
when the TERM
value has a -256color
suffix.
Some terminals also support full 24-bit colors, and any X11 color code can be written directly into a special escape sequence. (More infos) Only a few programs make use of anything beyond 256 colors, and tput doesn't know about them. Colors beyond 16 usually only apply to modern terminal emulators running in graphical environments.
The Virtual Terminal implemented in the Linux kernel supports only 16 colors, and the usual default terminfo entry for TERM=linux
defines only 8. There is sometimes an alternate “linux-16color” that you can switch to, to get the other 8 colors.
Bash examples
Hardcoded colors
printf '%b\n' 'It is \033[31mnot\033[39m intelligent to use \033[32mhardcoded ANSI\033[39m codes!'
Colors using tput
Directly inside the echo:
echo "TPUT is a $(tput setaf 2)nice$(tput setaf 9) and $(tput setaf 5)user friendly$(tput setaf 9) terminal capability database."
With preset variables:
COL_NORM="$(tput setaf 9)" COL_RED="$(tput setaf 1)" COL_GREEN="$(tput setaf 2)" echo "It's ${COL_RED}red${COL_NORM} and ${COL_GREEN}green${COL_NORM} - have you seen?"
Misc
HOME function
home() { # yes, actually not much shorter ;-) tput home }
Silly but nice effect
#!/bin/bash DATA[0]=" _/ _/ _/ _/ " DATA[1]=" _/_/_/_/_/ _/_/_/ _/_/_/ _/_/_/ _/_/_/ " DATA[2]=" _/ _/ _/ _/ _/ _/ _/_/ _/ _/" DATA[3]="_/_/_/_/_/ _/ _/ _/ _/ _/_/ _/ _/ " DATA[4]=" _/ _/ _/_/_/ _/_/_/ _/_/_/ _/ _/ " # virtual coordinate system is X*Y ${#DATA} * 5 REAL_OFFSET_X=0 REAL_OFFSET_Y=0 draw_char() { V_COORD_X=$1 V_COORD_Y=$2 tput cup $((REAL_OFFSET_Y + V_COORD_Y)) $((REAL_OFFSET_X + V_COORD_X)) printf %c ${DATA[V_COORD_Y]:V_COORD_X:1} } trap 'exit 1' INT TERM trap 'tput setaf 9; tput cvvis; clear' EXIT tput civis clear while :; do for ((c=1; c <= 7; c++)); do tput setaf $c for ((x=0; x<${#DATA[0]}; x++)); do for ((y=0; y<=4; y++)); do draw_char $x $y done done done done
Mandelbrot set
This is a slightly modified version of Charles Cooke's colorful Mandelbrot plot scripts ( original w/ screenshot) – ungolfed, optimized a bit, and without hard-coded terminal escapes. The colorBox
function is memoized to collect tput
output only when required and output a new escape only when a color change is needed. This limits the number of tput
calls to at most 16, and reduces raw output by more than half. The doBash
function uses integer arithmetic, but is still ksh93-compatible (run as e.g. bash ./mandelbrot
to use it). The ksh93-only floating-point doKsh
is almost 10x faster than doBash
(thus the ksh shebang by default), but uses only features that don't make the Bash parser crash.
#!/usr/bin/env ksh # Charles Cooke's 16-color Mandelbrot # http://earth.gkhs.net/ccooke/shell.html # Combined Bash/ksh93 flavors by Dan Douglas (ormaaj) function doBash { typeset P Q X Y a b c i v x y for ((P=10**8,Q=P/100,X=320*Q/cols,Y=210*Q/lines,y=-105*Q,v=-220*Q,x=v;y<105*Q;x=v,y+=Y)); do for ((;x<P;a=b=i=c=0,x+=X)); do for ((;a**2+b**2<4*P**2&&i++<99;a=((c=a)**2-b**2)/P+x,b=2*c*b/P+y)); do : done colorBox $((i<99?i%16:0)) done echo done } function doKsh { integer i float a b c x=2.2 y=-1.05 X=3.2/cols Y=2.1/lines while for ((a=b=i=0;(c=a)**2+b**2<=2&&i++<99&&(a=a**2-b**2+x,b=2*c*b+y);)); do : done . colorBox $((i<99?i%16:0)) if ((x<1?!(x+=X):(y+=Y,x=-2.2))); then print ((y<1.05)) fi do : done } function colorBox { (($1==lastclr)) || printf %s "${colrs[lastclr=$1]:=$(tput setaf "$1")}" printf '\u2588' } unset -v lastclr ((cols=$(tput cols)-1, lines=$(tput lines))) typeset -a colrs trap 'tput sgr0; echo' EXIT ${KSH_VERSION+. doKsh} ${BASH_VERSION+doBash}
A much more sophisticated version by Roland Mainz can be found here