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Terminal codes (ANSI/VT100) introduction
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 coordinates:!: it 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