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Styled output can viewed fine in a console or terminal emulator window.
The stylable program will typically have the following options:
--color
Use colors and other text attributes always.
--color=when
Use colors and other text attributes if when. when may be
always
, never
, auto
, or html
.
--style=style-file
Specify the CSS style rule file for --color
.
For more details, see the sections The --color
option and
The --style
option below.
If the output does not fit on a screen, you can use ‘less -R’ to scroll around in the styled output. For example:
program --color arguments | less -R |
TERM
The environment variable TERM
contains a identifier for the text
window's capabilities. You can get a detailed list of these cababilities
by using the ‘infocmp’ command (for example: infocmp -L1 xterm
),
using ‘man 5 terminfo’ as a reference.
When producing text with embedded color directives, a
libtextstyle
-enabled program looks at the TERM
variable.
Text windows today typically support at least 8 colors. Often, however,
the text window supports 16 or more colors, even though the TERM
variable is set to a identifier denoting only 8 supported colors. It
can be worth setting the TERM
variable to a different value in
these cases.
After setting TERM
, you can verify how well it works by invoking
‘program --color=test’, where program
is any
libtextstyle
-enabled program, and seeing whether the output looks
like a reasonable color map.
The following terminal emulator programs support 256 colors and set
TERM=xterm-256color
accordingly:
gnome-terminal
, tilda
.
rxvt-unicode
(sets TERM=rxvt-unicode-256color
).
st
(sets TERM=st-256color
).
QTerminal
.
Terminal
, iTerm2
.
The following terminal emulator programs support 256 colors. You only
need to set TERM=xterm-256color
or similar; the programs by default
set TERM
to a value that supports only 8 colors.
xterm
is in many cases built with support for 256 colors. But it
sets TERM=xterm
. You need to set TERM=xterm-256color
.
guake
(sets TERM=xterm
). You need to set
TERM=xterm-256color
.
konsole
(sets TERM=xterm
). You need to set
TERM=xterm-256color
or TERM=konsole-256color
.
yakuake
(sets TERM=xterm
). You need to set
TERM=xterm-256color
.
Eterm
(sets TERM=Eterm
). You need to set
TERM=Eterm-256color
.
mlterm
(sets TERM=mlterm
). You need to set
TERM=mlterm-256color
.
PuTTY
(sets TERM=xterm
). You need to set
TERM=xterm-256color
or TERM=putty-256color
.
TeraTerm
(sets TERM=xterm
). You need to set
TERM=xterm-256color
.
A couple of terminal emulator programs support even the entire RGB color space (16 million colors). To get this to work, at this date (2019), you need three things:
ncurses
library version 6.1 or newer must be installed.
TERM
environment variable to the corresponding
value:
TERM=xterm-direct
instead of
TERM=xterm
or TERM=xterm-256color
,
TERM=konsole-direct
in konsole
,
TERM=st-direct
in st
,
TERM=mlterm-direct
in mlterm
,
or TERM=iterm2-direct
in iTerm2
on macOS.
On OpenBSD 6 consoles, TERM=xterm
produces better results than the
default TERM=vt220
.
On NetBSD 8 consoles, TERM=netbsd6
produces better results than the
default TERM=vt100
.
On Windows consoles, no TERM
setting is needed.
NO_COLOR
The environment variable NO_COLOR
can be used to suppress styling
in the textual output. When this environment variable is set (to any value),
libtextstyle
-enabled programs will not emit colors and other text
styling.
This environment variable can be overridden by passing the command-line option
‘--color=always’ (see The --color
option).
NO_TERM_HYPERLINKS
The environment variable NO_TERM_HYPERLINKS
can be used to suppress
hyperlinks in the textual output. When this environment variable is set
(to any value), libtextstyle
-enabled programs will not emit
hyperlinks. This may be useful for terminal emulators which produce
garbage output when they receive the escape sequence for a hyperlink.
Currently (as of 2019), this affects some versions of
konsole
, emacs
, lxterminal
, guake
, yakuake
, rxvt
.
Emacs has several terminal emulators: M-x shell
and
M-x term
. M-x term
has good support for styling, whereas
in M-x shell
most of the styling gets lost.
--color
option The ‘--color=when’ option specifies under which conditions styled (colorized) output should be generated. The when part can be one of the following:
always
yes
The output will be colorized.
never
no
The output will not be colorized.
auto
tty
The output will be colorized if the output device is a tty, i.e. when the output goes directly to a text screen or terminal emulator window.
html
The output will be colorized and be in HTML format. This value is only supported by some programs.
test
This is a special value, understood only by some programs. It is
explained in the section (The environment variable TERM
) above.
‘--color’ is equivalent to ‘--color=yes’. The default is ‘--color=auto’.
Thus, a command that invokes a libtextstyle
-enabled program will
produce colorized output when called by itself in a command window.
Whereas in a pipe, such as ‘program arguments | less -R’,
it will not produce colorized output. To get colorized output in this
situation nevertheless, use the command
‘program --color arguments | less -R’.
The ‘--color=html’ option will produce output that can be viewed in a browser. This can be useful, for example, for Indic languages, because the renderic of Indic scripts in browsers is usually better than in terminal emulators.
Note that the output produced with the --color
option is
not consumable by programs that expect the raw text. It contains
additional terminal-specific escape sequences or HTML tags. For example,
an XML parser will give a syntax error when confronted with a colored XML
output. Except for the ‘--color=html’ case, you therefore normally
don't need to save output produced with the --color
option in a
file.
--style
option The ‘--style=style_file’ option specifies the style file to
use when colorizing. It has an effect only when the --color
option is effective.
If the --style
option is not specified, the program may consider
the value of an environment variable. It is meant to point to the user's
preferred style for such output. The name of such an environment
variable, if supported, is documented in the documentation of the
libtextstyle
-enabled program.
You can also design your own styles. This is described in the next section.
The same style file can be used for styling a certain type of output, for terminal output and for HTML output. It is written in CSS (Cascading Style Sheet) syntax. See https://www.w3.org/TR/css2/cover.html for a formal definition of CSS. Many HTML authoring tutorials also contain explanations of CSS.
In the case of HTML output, the style file is embedded in the HTML output.
In the case of text output, the style file is interpreted by the
libtextstyle
-enabled program.
You should avoid @import
statements, because
@import
statements would not be embedded in the HTML output. In fact, relative
file names would be interpreted relative to the resulting HTML file.
@import
s are not supported, due to a
limitation in libcroco
.
CSS rules are built up from selectors and declarations. The declarations specify graphical properties; the selectors specify when they apply.
GNU libtextstyle supports simple selectors based on "CSS classes", see
the CSS2 spec, section 5.8.3. The set of CSS classes that are supported
by a libtextstyle
-enabled program are documented in the
documentation of that program.
These selectors can be combined to hierarchical selectors. For example,
assume a program supports the CSS classes string
(that matches a
string) and non-ascii
(that matches a word with non-ASCII
characters), you could write
.string .non-ascii { color: red; } |
to highlight only the non-ASCII words inside strings.
In text mode, pseudo-classes (CSS2 spec, section 5.11) and pseudo-elements (CSS2 spec, section 5.12) are not supported.
The declarations in HTML mode are not limited; any graphical attribute supported by the browsers can be used.
The declarations in text mode are limited to the following properties. Other properties will be silently ignored.
color
(CSS2 spec, section 14.1)background-color
(CSS2 spec, section 14.2.1)These properties are supported. Colors will be adjusted to match the terminal's capabilities. Note that many terminals support only 8 colors.
font-weight
(CSS2 spec, section 15.2.3)This property is supported, but most terminals can only render two
different weights: normal
and bold
. Values >= 600 are
rendered as bold
.
font-style
(CSS2 spec, section 15.2.3)This property is supported. The values italic
and oblique
are rendered the same way.
text-decoration
(CSS2 spec, section 16.3.1)This property is supported, limited to the values none
and
underline
.
If you want to understand why the style rules in a style file produce the output that you see, you can do so in three steps:
--color=html
,
redirecting the output to a file.
This technique allows you, in particular, to see which CSS declarations override which other CSS declarations from other CSS rules.
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This document was generated by Bruno Haible on July, 26 2020 using texi2html 1.78a.