Control codes

Control character

Control character or non-printing character (NPC), resp. riadiaci znak, je znak, resp. kodovy bod (code point, number) z tabulky znakov (character set), ktory nepredstavuje pisany symbol (printing character), ale ma specialny vyznam pre spracovanie textu. Preto sa im zvykne hovorit aj non-printing znaky.

V ASCII kodovani (zakladne, 7 bitove, obsahujuce 128 znakov) su znaky s kodom mensim ako 32, resp. z intervalu 0x00—0x1F, control characters (riadiace znaky), oznacovane tiez ako aj C0 control code set. Riadiacim znakom je aj kod 127, resp. 0x7F, (DEL). Rozsirene ASCII kodovanie (8 bitove, obsahujuce 256 znakov) pridava kody od 128 do 159, resp. 0x80—0x9F, ako control characters. Tato druha sada riadiacich kodov sa oznacuje ako C1 set. Tychto 65 control characters (po 32 z C0 a C1 + znak DEL) bolo zahrnutych aj do Unicode znakovej sady, ktora pridava navyse este niektore vlastne riadiace znaky. Control characters sa tiez niekedy nazyvaju aj ako format effectors (formatovacie znaky).

Caret notation je sposob zapisu control characters, ktore su non-printable characters, v ASCII kodovani. Zapis zacina caret znakom ^ a velkym pismenom abecedy. Nulty symbol (NULL) sa zapisuju ako ^@ (znak @ je v ASCII tabulke pred znakom A), prvy control code (Start of Heading) ako ^A, druhy control code (Start of Text) ako ^B a podobne. Pre zapis mimo rozsahu 1-26 (A-Z) sa pouzivaju non-alphabetic ASCII characters. Takyto sposob zapisu sa niekedy tiez oznacuje ako Ctrl-Key.

Some popular ASCII control codes (C0)
Caret	Decimal	Octal	Hex	C escape	Abbreviation	Name
`^@`	00	000	0x00	`\0`	NUL	Null character
`^G`	07	007	0x07	`\a`	BEL	Bell, Alert
`^H`	08	010	0x08	`\b`	BS	Backspace
`^I`	09	011	0x09	`\t`	HT	Horizontal TAB
`^J`	10	012	0x0A	`\n`	LF	Line Feed (new line)
`^K`	11	013	0x0B	`\v`	VT	Vertical TAB
`^L`	12	014	0x0C	`\f`	FF	Form Feed (page break)
`^M`	13	015	0x0D	`\r`	CR	Carriage Return
`^[`	27	033	0x1B	`\e`^*	ESC	Escape
`^?`	127	177	0x7F		DEL	Delete
NOTE C escape sequence `\e` nie je sucastou ISO C ani ostatnych prog. jazykov, ale napr. gcc ho podporuje. Odporuca sa pouzivat napr. hex prezentaciu.

$ echo -ne '\n' | od -t c -t d1 -t o1 -t x1   # od(1)
0000000   \n
          10
         012
          0a
0000001

ANSI escape code

https://en.wikipedia.org/wiki/ANSI_escape_code

Rozsirujuci kod spomedzi control characters je ASCII escape character (27, resp. 033, resp. 0x1B, ESC, ^[, \e). Escape sequences (escape postupnosti) je kod vlozeny v text pre rozne formatovanie (farba, styl fontu) vystupu na na textovy terminal (emulator) alebo aj napr. na ovladanie kurzora. Umoznuje pozmenit standardne spravanie terminalov, napr. zmazanie obrazovky, farebny vypis, zmena pozicie kurzora a podobne. Do textu sa vkladaju (zakoduju) urcite postupnosti bytes (znakov), ktore terminal neinterpretuje ako kody znakov (text), ale ako prikazy. Historicky existovala mnozstvo terminalov s roznymi postupnostami (a k tomu este proprietarnymi), preto sa dnes pouziva zavedeny ANSI standard.

Escape sequences maju roznu dlzku a pozostavaju iba zo znakov z rozsahu 32—126, resp. 0x20—0x7E, t.j. zo vsetkych non-control characters, resp. vsetky printable characters. Ak by znak bol mimo daneho rozsahu, spravanie terminalu nie je definovane.

ANSI Escape sequences with ASCII (7-bit) byte
Name	Decimal	Hex	Usage example
nF Escape sequences	32—47	0x20—0x2F	used for ANSI/ISO code-switching mechanisms
Fp Escape sequences	48—63	0x30—0x3F	up to sixteen private-use control functions
Fe Escape sequences	64—95	0x40—0x5F	most used, for example CSI (with SGR) or OSC sequences
Fs Escape sequences	96—126	0x60—0x7E	used for control functions individually registered with the ISO-IR registry

Fe Escape sequences

Ak po ESC nasleduje byte z rozsahu 0x40 az 0x5F, escape sequence je typu Fe. Typickym predstavitelom je postupnost ESC[ (Control Sequence Introducer), pripadne ESC] (Operating System Command). Prostredie, ktore podporuje iba ASCII (7-bit), rozpoznava iba dvoj-znakovu postupnost. Standard vsak umoznuje, v 8-bit prostredi, aj jedno-znakovu escape sequence z rozsahu 0x80—0x9F, t.j. C1 control code set. Napr. existuje aj jedno-znakove CSI (155, resp. 0x9B), ale dvoj-znakova postupnost ESC[ sa pouziva castejsie. V sucasnosti sa na modernych zariadeniach, ako napr. UTF-8 alebo CP-1252, jedno-znakove kody pouzivaju na ine ucely, a zvycajne sa pouziva iba dvoj-znakova postupnost.

NOTES

Niektore kodovania mozu pouzivat viac ako jeden byte na znak, v dalsom budeme predpokladat pouzivanie len ASCII znakov, ktore su reprezentovane prave jednym byte (jeden byte, jeden znak).
Niektore kody z C0 control set (teda okrem ESC), mozu mat rovnaky, podobny efekt ako niektore escape sequence.
Dalej, pokial nebude uvedene inak, budeme predpokladat default prostredie pre Fedora Linux: GNU bash, pouzivanie terminal emulatora GNOME Terminal, TERM="xterm-256color", COLORTERM="truecolor", LANG="en_US.UTF-8".

Control codes in shell script

Prikaz echo with option -e (enable interpretation of backslash-escaped characters) nie je POSIX, a teda, stracame portabilitu. Vseobecne sa odporuca nahradzat prikaz echo -e prikazom printf (formatuje ako C printf), ale kedze echo prikaz je extremne rozsireny napriec celym Linux (Unix) svetom, je pouzivanie echo -e "pripustne". Obidva prikazy rozpoznavaju standardne sequences, ako napr. \b, \n, \t, \e a podobne. Okrem toho umoznuju zadavat priamo control codes ako octal, hexadecimal alebo Unicode znaky s hex hodnotami. Ako uz bolo spomenute, POSIX odporuca uprednostnovat printf namiesto echo, obzvlast v pripade echo -e.

NOTE V praxi sa vacsinou pouzivaju builtin prikazy echo a printf shell prostredia a nie ich standalone ekvivalent. Ako dosledok toho, builtin prikaz echo vie spracovat aj Unicode znaky na rozdiel od standalone verzie (standalone man echo vs. echo in man builtins).

# in all cases absolute identically output
$ echo -ne '\t';   echo -ne '\011';    echo -ne '\x09';   echo -ne '\u0009'
$ printf '\t';     printf '\011';      printf '\x09';     printf '\u0009'

NOTE Interpretacia octal value nnn (zero to three octal digits) je pre prikaz echo -e v tvare \0nnn, ale pre printf v tvare \nnn (nezacina nulou). Takze pre prikaz echo -e plati '\0011' = '\011' ≠ '\11', ale pre prikaz printf plati '\011' = '\11' ≠ '\0011'. Zapisy pre hex, resp. Unicode hodnoty su identicke v oboch pripadoch a preto su preferovane.

NOTE Prikaz printf interpretuje number format 0N, t.j. integer cislo zacinajuce nulou ako octal hodnotu, preto printf '%d' 11 vypise 11 ale printf '%d' 011 vypise ako 9. Nezamienat, nepliest si s formatom \nnn pre escape codes, ktore zacina znakom \ (backslash).

Pre zobrazenie standardneho vystupu sa najbeznejsie pouzivaju prikazy cat(1) a less(1), ktory nahradza dnes uz zastarany more(1). Prikaz less zobrazuje vacsinu control codes znakov by default (option -U pridava navyse aj backspaces, tabs and carriage returns) a pre zobrazenie ANSI "color" escape sequences je potrebne pouzit option -R. Naopak, prikaz cat by default zobrazuje "farebne" a pre zobrazenie non-printing bytes, znakov je potrebne pouzit option -v alebo rovno -A. Citame man stranky.

$ echo -ne '\t' | cat -A
^I
$ printf '\u0009' | less -U --quit-if-one-screen     # --quit-if-one-screen = -F
^I

Moderny Bash este ponuka moznost zapisu pomocou ANSI-C Quoting, kedy je zapis $string specialne osetreny (nie je POSIX). Backslash \ escape sequences su dekodovane ako ANSI C standard. Kedze je to Bash rozsirenie, nie je podstatne, ci pouzijem prikaz printf alebo echo (without option -e). Pouzivanie ANSI-C Quoting s printf je skor ojedinele, kedze prikaz sam o sebe formatuje ako C printf.

NOTE Bash ANSI-C Quoting dekoduje octal value v tvare \nnn (one to three octal digits).

$ bla1=$'\011'; bla2=$'\11'; bla3=$'\t'
$ (echo -n "$bla1"; echo -n "$bla2"; echo -n "$bla3") | cat -A
^I^I^I
$ (printf "$bla1"; printf "$bla2"; printf "$bla3") | less -U --quit-if-one-screen
^I^I^I

CSI (Control Sequence Introducer) sequences

Jedna z najpouzivanejsich escape sequences je Control Sequence Introducer (CSI), t.j. sequences ESC[, resp. ^[[ (napisane ako \e[, \033[ alebo \x1b[), za ktorou nasleduje nejaky lubovolny pocet bytes z rozsahu urcenom pre escape sequences, t.j. z rozsahu 32—126, resp. 0x20—0x7E. Znova plati, ak je byte (znak) mimo daneho rozsahu, spravanie terminalu nie je definovane. CSI je definovana ako sequences ESC[ nasledovana lubovolnym (alebo ziadnym) poctom parameter bytes, nasledovana lubovolnym (alebo ziadnym) poctom intermediate bytes, a na koniec, nasledovana jednym final byte (vid tabulka).

CSI (Control Sequence Introducer) sequences `ESC[` followed by
none or any numbers of parameter bytes	none or any numbers of intermediate bytes	single final byte
0x30—0x3F	0x20—0x2F	0x40—0x7E
48—63	32—47	64—126
`0–9:;<=>?`	`space !"#$%&'()*+,-./`	@A–Z[\]^_`a–z{\|}~
subset of private bytes^*
`<=>?`		`p–z{\|}~`
reserved byte^* for future standardization
`:`
typically used bytes
`0–9;`	are not usually used	`A–Za–o`
NOTE A subset of bytes was declared "private" so that terminal manufacturers could insert their own sequences without conflicting with the standard. NOTE All escape sequences with "reserved" byte `:` must be ignored. It was left for future standardization.

Typicka CSI sequences je CSI n1;n2;... (intermediate bytes) final byte. Final byte je pismeno urcujuce prikaz (funkciu). Cisla(o) n su parametre tohto prikazu (funkcie) oddelene bodkociarkou (semicolon). Final byte moze byt modifikovany pouzitim intermediate bytes, ale zvycajne sa nepouzivaju. Cisla n nie su povinne parametre, a pokial su vynechane, ich implicitna hodnota zavisi od prikazu, ale obycajne je to 0 alebo 1. Sekvenciu 1;2;3 mozno zapisat aj ako 1;;3, kedy sa za prostredne cislo bude povazovat 0 pripadne 1.

SGR (Select Graphic Rendition) parameters

Escape sequence s ktorou sa uzivatel asi najskor stretne je control sequence CSInm, nazyvana ako Select Graphic Rendition (SGR), a ktora nastavuje rozne hodnoty zobrazenia (terminal zobrazuje farebne). Niekolko atributov moze byt nastavenych spolu v tej istej sekvencii n₁;n₂;n₃;... oddelenych navzajom bodkociarkou (semicolon). Kazdy atribut zobrazenia zostava v platnosti, pokial ho nasledujuca SGR sekvencia nezmeni, resp. neresetuje. Vynechany, resp. ziaden parameter v SGR sequence CSIm sa interpretuje ako CSI0m, t.j. reset vsetkych atributov na ich default hodnotu. SGR sa tiez zvykne oznacovat aj ako ANSI color escape sequences.

Examples

Code	Abbr	Name	Effect
`ESC [ n D`	CUB	Cursor Back	Moves the cursor n (default `1`) cells in the left.
`ESC [ n K`	EL	Erase in Line	Erases part of the line. If n is `0` (or missing), clear from cursor to the end of the line. If n is `1`, clear from cursor to beginning of the line. If n is `2`, clear entire line. Cursor position does not change.
`ESC [ n m`	SGR	Select Graphic Rendition	Sets display attributes (colors and style) of the characters following this code.

# we will mainly use hexadecimal notation '\x1b'

$ printf '1234567890\x1b[Dafter\n'
123456789after
$ printf '1234567890\x1b[8Dafter\n'
12after890
$ printf '1234567890\x1b[8D\x1b[Kafter\n'
12after
$ printf '1234567890\x1b[8D\x1b[1Kafter\n'
  after890

$ CUB3='\x1b[3D'
$ printf '12345%b#\n12345%b\x1b[K\n12345%b\x1b[1K\n' "$CUB3" "$CUB3" "$CUB3"
12#45
12
   45

# example of DEC private mode sequences (DECTECM)
$ printf '\x1b[?25l'   # cursor invisible
$ printf '\x1b[?25h'   # cursor visible (by default)

$ SGR='\x1b[%bm'     # SGR with parameter(s)
$ printf 'normal'"$SGR"'effect'"$SGR"'reset\n' "4" "0"
normaleffectreset
$ printf 'normal'"$SGR"'effect'"$SGR"'reset\n' "3;31" "0"
normaleffectreset
$ printf 'normal'"$SGR"'effect'"$SGR"'reset\n' "1;32;41" "0"
normaleffectreset
$ printf 'normal'"$SGR"'effect'"$SGR"'reset\n' "1;3;4;35" "0"
normaleffectreset

$ printf "normal${SGR}effect${SGR}reset\n" "1" "0"

Code	Color	SGR Color depth	Note
`ESC [ 30+i m` `ESC [ 40+i m`	foreground background	3-bit (8 colors)	The original specification only had 8 basic colors; i ∈ <0, 7>
`ESC [ 90+i m` and 3-bit `ESC [ 100+i m` and 3-bit	foreground background	4-bit (16 colors)	Later terminals added another 8 "bright" colors; i ∈ <0, 7>
`ESC [ 38;5;n_i m` `ESC [ 48;5;n_i m`	foreground background	8-bit (256 colors)	n_i is a number from wiki table; i ∈ <0, 255>
`ESC [ 38;2;r_i;g_i;b_i m` `ESC [ 48;2;r_i;g_i;b_i m`	foreground background	24-bit (true colors)	About 16M of RGB colors; i ∈ <0, 255>

NOTE Moderny terminal vacsinou pouziva nejaku preddefinovanu paletu zakladnych 8/16 farieb z built-in schemes. GNOME Terminal by default pouziva "GNOME" palette schema, kde napr. zakladna modra (34/44) je RGB(18,72,139), ale napr. "Linux console" palette schema pouziva pre zakladnu modru RGB(0,0,170). Okrem toho, uzivatel si v principe moze kazdu zo zakladnych farieb nastavit podla uvazenia.

# GNOME Terminal with "Linux console" palette built-in schema

$ SGRC='\x1b[%bm'; SGRR='\x1b[0m'     # SGR with parameter (color) and reset
$ printf "$SGRC"'3-bit blue'"$SGRC"' 4-bit bright blue'"$SGRR"' reset\n'                  "34" "94"
3-bit blue 4-bit bright blue reset
$ printf "$SGRC"'8-bit standard blue'"$SGRC"' 8-bit high-intensity blue'"$SGRR"' reset\n' "38;5;4" "38;5;12"
8-bit standard blue 8-bit high-intensity blue reset
$ printf "$SGRC"'24-bit RGB(0,0,170)'"$SGRC"' 24-bit RGB(85,85,255)'"$SGRR"' reset\n'     "38;2;0;0;170" "38;2;85;85;255"
24-bit RGB(0,0,170) 24-bit RGB(85,85,255) reset

$ printf "$SGRC"'FG: 4-bit bright white, BG: 24-bit RGB(85,85,255)'"$SGRR"' reset\n' "97;48;2;85;85;255"
FG: 4-bit bright white, BG: 24-bit RGB(85,85,255) reset

$ printf "$SGRC"'FG: 4-bit bright white, BG: 24-bit RGB(85,85,255)'"$SGRR"' reset\n' "97;48;2;85;85;255" | cat -v
^[[97;48;2;85;85;255mFG: 4-bit bright white, BG: 24-bit RGB(85,85,255)^[[0m reset
$ printf "$SGRC"'FG: 4-bit bright white, BG: 24-bit RGB(85,85,255)'"$SGRR"' reset\n' "97;48;2;85;85;255" | less -F
ESC[97;48;2;85;85;255mFG: 4-bit bright white, BG: 24-bit RGB(85,85,255)ESC[0m reset

Examples commands

https://wiki.archlinux.org/title/Color_output_in_console

Niektore Linux prikazy vytvaraju control escape sequences output. Najbeznejsie sa stretneme s prikazmi ls(1) alebo grep(1), ktore umoznuje "colorize the output". Obidva prikazy pouzivaju option --color=auto (emits color codes only when standard output is connected to a terminal) by default . Pre experimentovanie je vhodnejsie pouzit --color=always option. Environment variable LS_COLORS, resp. GREP_COLORS umoznuje menit preddefinovane nastavenia.

Prikaz ls rozlisuje rozne farby pre rozne typy suborov. Environment variable LS_COLORS je nastavena (by default) prostrednictvom /etc/DIR_COLORS. Prikaz dircolors(1) nastavi (a vypise) hodnotu LS_COLORS. Viac info dir_colors(5).

$ mkdir ls_test; cd ls_test; touch 111.txt 222.gz 333.xz 444.dat zzz; mkdir dir555
$ ls
111.txt  222.gz  333.xz  444.dat  dir555  zzz

$ ls --color=always | less -F
111.txt
ESC[0mESC[01;31m222.gzESC[0m   # SGR reset → SGR effect → 222.gz → SGR reset
ESC[01;31m333.xzESC[0m         # SGR effect → 333.xz → SGR reset
444.dat
ESC[01;34mdir555ESC[0m         # SGR effect → dir555 → SGR reset
zzz

Prikaz grep pouziva environment variable GREP_COLORS='ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36' (hodnota by default). Viac info GREP_COLORS.

$ printf '111x222' | grep 'x'
111x222

$ printf '111x222' | grep --color=always 'x' | less -F
111ESC[01;31mESC[KxESC[mESC[K222   # 111 → SGR effect → EL default → x → SGR reset → EL default → 222
                                   # EL (Erase in Line) default = erase from cursor to the end of the line. Cursor position does not change. Capability ne from GREP_COLORS is false by default.

$ # export GREP_COLORS='mt=01;34'     # change only mt capability (others without changes)
$ # export GREP_COLORS=''             # reset all to default

$ printf '111x222' | GREP_COLORS='mt=32:ne' grep 'x'
111x222

$ printf '111x222' | GREP_COLORS='mt=32'    grep --color=always 'x' | less -F     # boolean capability ne (no EL) is false by default
111ESC[32mESC[KxESC[mESC[K222      # 111 → SGR effect → EL default → x → SGR reset → EL default → 222
$ printf '111x222' | GREP_COLORS='mt=32:ne' grep --color=always 'x' | less -F     # capability ne is true
111ESC[32mxESC[m222                # 111 → SGR effect → x → SGR reset → 222

NOTE Najlepsia dokumentacia je priamo zdrojovy kod grep.c. Vysvetlene, okrem ineho, preco vyvojari zaviedli (Why have EL to Right after SGR?) capability ne from GREP_COLORS a preco je by default false.

# replace SGR Escape sequences in color grep by using the backspace character, resp. by overstriking with backspaces (see bellow)

G_COLOR='\x1b\[31m' # SGR color
G_RESET='\x1b\[m'   # SGR reset
G_UNDER='_\x08'     # underline (overstriking with backspace)
printf '111x222' | GREP_COLORS='mt=31:ne' grep --color=always 'x' | sed -e "s/$G_COLOR/$G_UNDER/g" -e "s/$G_RESET//g" | less -F # -U

man page formatting

man-db package na Fedore implementuje rozne nastroje, resp. prikazy na prezeranie man stranok. Prikaz man(1) formatuje a zobrazuje manualove stranky. Package man-pages obsahuju samotne man stranky s obsahom. By default man pouziva terminal pager program less pre zobrazenie obsahu.

Default format pre man stranky je troff(1), ktory umoznuje spolu s roznymi makro balikmi formatovat pre rozne vystupy ako napr. TTY (stdout), PDF, html a pod. OpenBSD od roka 2010 pouziva mandoc namiesto troff pre formatovanie man stranok. Moderny Linux pouziva groff(7) (the GNU implementation of roff(7)). Tu zacina "terminologicka dzungla" roff, troff, nroff, groff, grotty a dalsie desiatky terminov, resp. prikazov. Jedina vyhoda, v pripade ak sa clovek rozhodne v tom vyznat, vsetko je podrobne zdokumentovane v man strankach. Existuje tu akasi paralela: TeXLive vs. groff, TeX vs. troff/roff atd.

man(7) vysvetluje ako sa pouzivaju makra pre formatovanie man stranok, ktore vytvara prikaz groff(1).

$ man -w git
/usr/share/man/man1/git.1.gz
$ zcat /usr/share/man/man1/git.1.gz | groff -T utf8 -m man                 # -m man = -man
$ zcat /usr/share/man/man1/git.1.gz | groff -T utf8 -m man | less -R       # less pager
$ zcat /usr/share/man/man1/git.1.gz | groff -T pdf  -m man > man_git.pdf   # dnf install groff-perl (provides gropdf, PDF postprocessor for groff)

-T utf8 set TTY output devices, text with UTF-8 encoding, postprocessor is grotty(1). -m man include man macro packages for traditional man page format, see groff_man(7). Existuju rozne vystupne zariadenia, napr. default PS (grops), PDF (gropdf), dvi (grodvi), html (grohtml) a samozrejme TTY output devices (grotty) s textom v roznom kodovani a zaroven existuju rozne macro packages, napr. man (groff_man), mdoc (groff_mdoc), me (groff_me), ms (groff_ms) a podobne, see groff_tmac(5).

NOTE Niekedy sa este zvykne pouziva prikaz nroff(1) - use groff to format documents for TTY devices. GNU nroff emulates the traditional Unix nroff command using groff. nroff generates output via grotty. V praxi je to shell script /usr/bin/nroff, resp. groff wrapper, ktory nastavi TTY output device s aktualne pouzivanim kodovanim. Pre Fedora Linux nroff = groff -mtty-char -Tutf8.

groff(7), resp. groff_man(7) obsahuju dokumentaciu pre strukturu, syntax, formatovanie, ktore sa pouziva, okrem ineho, pre man stranky. Prikazy roff jazyka (historically, the roff language was called troff) su v podstate len dvoch druhov.

requests sa pisu vzdy na vlastny riadok (roff je "line-oriented" jazyk, t.j. co riadok to prikaz) a zacinaju . alebo '.
escape sequences are in-line functions and in-word formatting elements zacinajuce \ (nezamienat s ANSI escape sequences).

Casto sa pouziva font escape sequence \f za ktorou nasleduje indikator B (bold), I (italic, underline) or R (regular, roman). Jednoduchy priklad man stranky, resp. roff jazyka, subor exam.roff (priklad na formatovanie a nie strukturu man stranok).

.TH EXAMPLE 1                           \" Title heading   (request)
.SH DESCRIPTION                         \" Section heading (request)
.B bold text                            \" bold            (request)
next \fBbold \fIitalic OR underline     \" bold, italic    (escape sequences)
\fRregular OR roman                     \" regular         (escape sequences)

$ groff -T utf8 -man exam.roff
DESCRIPTION
       bold text next bold italic OR underline regular OR roman

Man stranky v principe pouzivaju len tri sposoby formatovania textu, resp. font changes: regular, bold, italic/underline. Existuje moznost formatovat priamo aj farebny text, napr. \m[green]\fBgreen bold \fR\m[]reset → green bold reset, ale tato moznost sa dorazne neodporuca hlavne kvoli maximalnej portabilite (man stranky sa zobrazuju na velmi sirokom spektre zariadeni, terminalov). groff option -c disable color output, alebo inymi slovami, ignoruje \m escape sequence.

Prikaz groff, resp. grotty(1) postprocessor (zaujima nas vystup na terminal), by default, formatuje (zobrazuje) change text attributes (bold, italic/underline pripadne colors) pomocou SGR Escape sequence na TTY zariadeniach.

$ printf '.TH EXAM\n\\fBbold\\fIitalic\\fRregular' | groff -T utf8 -man
bolditalicregular
$ printf '.TH EXAM\n\\fBbold\\fIitalic\\fRregular' | groff -T utf8 -man | less -F      # less, by default, display control characters
ESC[1mboldESC[4mESC[22mitalicESC[24mregular   # SGR effect(1=bold) → bold → SGR effect(4=underline) → SGR effect(22=normal) → italic → SGR effect(24=not underlined) → regular
$ printf '.TH EXAM\n\\fBbold\\fIitalic\\fRregular' | groff -T utf8 -man | less -F -R   # less -R display SGR (ANSI escape sequences are output in "raw" form)
bolditalicregular

Existuje aj starsi, ale este stale pouzivany sposob pre zobrazenie bold a underline, from less FAQ: Some text files, notably Unix-style "man pages", use overstriking (backspaces) to simulate underlined and bold text. Less interprets this overstriking and displays the text in real underlined or bold mode. Tato analogia zobrazovania pochadza este z klasickych pisacich strojoch (typewriters).

bold use letter + backspace + letter sequences to indicate a letter should be displayed in bold face (a+backspace+a = a).
underline use underscore + backspace + letter sequences to indicate a letter should be displayed in underline face (_+backspace+a = a).

$ printf 'a\ba' | less -F # -U     # less -U display backspaces, tabs and carriage returns control characters
a   # a^Ha
$ printf '_\ba' | less -F # -U
a   # _^Ha

Niektore terminaly, napr. kterm, ale aj starsie verzie programu less (resp. without -R option) nevedia zobrazovat SGR Escape sequence. V pripade ak potrebujeme formatovat (zobrazit) man stranky starsim sposobom (using the backspace character), potrebujeme nastavit grotty(1) environment variable GROFF_NO_SGR alebo pouzit option -c (grotty -c = groff -P-c).

$ printf '.TH EXAM\n\\fBbold\\fIitalic\\fRregular' | GROFF_NO_SGR=1 groff -T utf8 -man      | less -F -U
$ printf '.TH EXAM\n\\fBbold\\fIitalic\\fRregular' |                groff -T utf8 -man -P-c | less -F -U
b^Hbo^Hol^Hld^Hd_^Hi_^Ht_^Ha_^Hl_^Hi_^Hcregular

$ zcat /usr/share/man/man1/git.1.gz | groff -T utf8 -man      | less      # using SGR Escape sequence (by default)
$ zcat /usr/share/man/man1/git.1.gz | groff -T utf8 -man -P-c | less -U   # using the backspace character (SGR disabled) or set GROFF_NO_SGR

Prave tento starsi sposob zobrazovania (using the backspace character) sa da vyuzit na "farebne" zobrazovanie man stranok. "Farebne" znamena len jednoduchu zamenu bold a underline text attributes na nejaku nami definovanu farbu. Tuto zamenu umoznuje option -D (or long --color) programu less, ktory je terminal pager program pre man stranky. Samotne man stranky su formatovane bez farby aj napriek tomu, ze tato moznost existuje (vid vyssie), ale z dovodu maximalnej portability sa vsak neodporuca.

$ zcat /usr/share/man/man1/git.1.gz | groff -T utf8 -man -P-c | less --color=d+r --color=u+b   # color man page (bold+red and underline+blue)

$ printf '.TH EXAM\n\\fBbold\\fIitalic\\fRregular' | GROFF_NO_SGR=1 groff -T utf8 -man | less -F -Dd+y -Dur
bolditalicregular

Pozorne citame less(1) man stranky. -Dur change color for underlined text (u) on red (r), -Dd+y change bold text (d) on yellow (y) color and (+) displays bold text as both yellow and in bold format. Podstatne je, ze tento "change color" pracuje iba pre formatovanie (zobrazovanie) vytvorene starsim sposobom (using the backspace character, resp. by overstriking with backspaces) a nie pre text formatovany cez SGR Escape sequence, co je by default sposob pre groff. Prave preto je potrebne pouzit grotty environment variable GROFF_NO_SGR alebo option -c. Kedze uz mame farebny vystup je vhodne pouzit aj option --use-color, ktora "zafarbi" aj samotny program less (stavovy riadok, vyhladavanie a podobne).

Summarum Color for man pages (MANROFFOPT and MANPAGER are man environment variables)

$ MANROFFOPT='-c' MANPAGER='less -Dd+y -Dur --use-color' man git

or export variables (use of LESS_TERMCAP_* variables is not necessary).

export MANROFFOPT='-c'           # or GROFF_NO_SGR='1'
export MANPAGER='less -Dd+y -Dur --use-color'

Bash color prompt

NOTE for Bash prompt use C escape \e[ or octal \033[ CSI notation (hex \x1b[ not working).

PS1='[\u@\h \W]\$ '                     # traditional prompt
PS1='[\u@\h_\e[44m_BLUE_\e[0m_\W]\$ '   # add colored BLUE word !!! don't use !!! (works but with issues)

bash(1) recommended wrapping output in \[ and \] (use \[\e[COLORm\] instead of \e[COLORm), this helps Bash ignore non-printable characters. The wrap will not work for surrounding non-printable characters (command substitution). Instead you can use the octal escapes \001 and \002 (use \001\e[COLORm\002). More info [1] or [2].

PS1='[\u@\h_\[\e[44m\]_BLUE_\[\e[0m\]_\W]\$ '           # OK
PS1='[\u@\h_\001\e[44m\002_BLUE_\001\e[0m\002_\W]\$ '   # OK (more universal)