nano: Syntax Highlighting
8.2 Syntax Highlighting
=======================
Coloring the different syntactic elements of a file is done via regular
expressions (see the ‘color’ command below). This is inherently
imperfect, because regular expressions are not powerful enough to fully
parse a file. Nevertheless, regular expressions can do a lot and are
easy to make, so they are a good fit for a small editor like ‘nano’.
See ‘/usr/share/nano/’ and ‘/usr/share/nano/extra/’ for the
syntax-coloring definitions that are available out of the box.
All regular expressions in ‘nano’ are POSIX extended regular
expressions (ERE). This means that ‘.’, ‘?’, ‘*’, ‘+’, ‘^’, ‘$’, and
several other characters are special. The period ‘.’ matches any single
character, ‘?’ means the preceding item is optional, ‘*’ means the
preceding item may be matched zero or more times, ‘+’ means the
preceding item must be matched one or more times, ‘^’ matches the
beginning of a line, and ‘$’ the end, ‘\<’ matches the start of a word,
and ‘\>’ the end, and ‘\s’ matches a blank. It also means that
lookahead and lookbehind are not possible. A complete explanation can
be found in the manual of GNU grep: ‘info grep regular’.
A separate syntax can be defined for each kind of file via the
following commands in a nanorc file:
‘syntax NAME ["FILEREGEX" ...]’
Start the definition of a syntax with this NAME. All subsequent
‘color’ and other such commands will be added to this syntax, until
a new ‘syntax’ command is encountered.
When ‘nano’ is run, this syntax will be automatically activated if
the current filename matches the extended regular expression
FILEREGEX. Or the syntax can be explicitly activated by using the
‘-Y’ or ‘--syntax’ command-line option followed by the NAME.
The ‘default’ syntax is special: it takes no FILEREGEX, and applies
to files that don’t match any syntax’s regexes. The ‘none’ syntax
is reserved; specifying it on the command line is the same as not
having a syntax at all.
‘header "REGEX" ...’
If from all defined syntaxes no FILEREGEX matched, then compare
this REGEX (or regexes) against the first line of the current file,
to determine whether this syntax should be used for it.
‘magic "REGEX" ...’
If no FILEREGEX matched and no ‘header’ regex matched either, then
compare this REGEX (or regexes) against the result of querying the
‘magic’ database about the current file, to determine whether this
syntax should be used for it. (This functionality only works when
‘libmagic’ is installed on the system and will be silently ignored
otherwise.)
‘formatter PROGRAM [ARGUMENT ...]’
Run the given PROGRAM on the full contents of the current buffer.
(The current buffer is written out to a temporary file, the program
is run on it, and then the temporary file is read back in,
replacing the contents of the buffer.)
‘linter PROGRAM [ARGUMENT ...]’
Use the given PROGRAM to do a syntax check on the current buffer.
‘comment "STRING"’
Use the given string for commenting and uncommenting lines. If the
string contains a vertical bar or pipe character (|), this
designates bracket-style comments; for example, "/*|*/" for CSS
files. The characters before the pipe are prepended to the line
and the characters after the pipe are appended at the end of the
line. If no pipe character is present, the full string is
prepended; for example, "#" for Python files. If empty double
quotes are specified, the comment/uncomment functions are disabled;
for example, "" for JSON. The default value is "#".
‘tabgives "STRING"’
Make the <Tab> key produce the given STRING. Useful for languages
like Python that want to see only spaces for indentation. This
overrides the setting of the ‘tabstospaces’ option.
‘color [bold,][italic,]FGCOLOR,BGCOLOR "REGEX" ...’
Paint all pieces of text that match the extended regular expression
"regex" with the given foreground and background colors, at least
one of which must be specified. Valid color names are: ‘red’,
‘green’, ‘blue’, ‘magenta’, ‘yellow’, ‘cyan’, ‘white’, and ‘black’.
Each of these eight names may be prefixed with the word ‘light’ to
get a brighter version of that color. The word ‘grey’ or ‘gray’
may be used as a synonym for ‘lightblack’.
On terminal emulators that can do at least 256 colors, other valid
(but unprefixable) color names are: ‘pink’, ‘purple’, ‘mauve’,
‘lagoon’, ‘mint’, ‘lime’, ‘peach’, ‘orange’, ‘latte’, ‘rosy’,
‘beet’, ‘plum’, ‘sea’, ‘sky’, ‘slate’, ‘teal’, ‘sage’, ‘brown’,
‘ocher’, ‘sand’, ‘tawny’, ‘brick’, ‘crimson’, and ‘normal’ — where
‘normal’ means the default foreground or background color. On such
emulators, the color may also be specified as a three-digit
hexadecimal number prefixed with ‘#’, with the digits representing
the amounts of red, green, and blue, respectively. This tells
‘nano’ to select from the available palette the color that
approximates the given values.
The color pair may be preceded by ‘bold’ and/or ‘italic’ (separated
by commas) to get a bold and/or slanting typeface, if your terminal
can do those.
All coloring commands are applied in the order in which they are
specified, which means that later commands can recolor stuff that
was colored earlier.
‘icolor [bold,][italic,]FGCOLOR,BGCOLOR "REGEX" ...’
Same as above, except that the matching is case insensitive.
‘color [bold,][italic,]FGCOLOR,BGCOLOR start="FROMRX" end="TORX"’
Paint all pieces of text whose start matches extended regular
expression "fromrx" and whose end matches extended regular
expression "torx" with the given foreground and background colors,
at least one of which must be specified. This means that, after an
initial instance of "fromrx", all text until the first instance of
"torx" will be colored. This allows syntax highlighting to span
multiple lines.
‘icolor [bold,][italic,]FGCOLOR,BGCOLOR start="FROMRX" end="TORX"’
Same as above, except that the matching is case insensitive.
‘include "SYNTAXFILE"’
Read in self-contained color syntaxes from "syntaxfile". Note that
"syntaxfile" may contain only the above commands, from ‘syntax’ to
‘icolor’.
‘extendsyntax NAME COMMAND ARGUMENT ...’
Extend the syntax previously defined as "NAME" with another
COMMAND. This allows you to add a new ‘color’, ‘icolor’, ‘header’,
‘magic’, ‘formatter’, ‘linter’, ‘comment’, or ‘tabgives’ command to
an already defined syntax — useful when you want to slightly
improve a syntax defined in one of the system-installed files
(which normally are not writable).
Info Catalog
nano: Settings
nano: Nanorc Files
nano: Rebinding Keys