FcPatternFormat(3) FcPatternFormat(3)

NAME

FcPatternFormat - Format a pattern into a string according to a
format specifier

SYNOPSIS

#include <fontconfig/fontconfig.h>

FcChar8 * FcPatternFormat (FcPattern *pat, const FcChar8 *format);

DESCRIPTION

Converts given pattern pat into text described by the format
specifier format. The return value refers to newly allocated memory
which should be freed by the caller using free(), or NULL if format
is invalid.

The format is loosely modeled after printf-style format string. The
format string is composed of zero or more directives: ordinary
characters (not "%"), which are copied unchanged to the output
stream; and tags which are interpreted to construct text from the
pattern in a variety of ways (explained below). Special characters
can be escaped using backslash. C-string style special characters
like \n and \r are also supported (this is useful when the format
string is not a C string literal). It is advisable to always escape
curly braces that are meant to be copied to the output as ordinary
characters.

Each tag is introduced by the character "%", followed by an optional
minimum field width, followed by tag contents in curly braces ({}).
If the minimum field width value is provided the tag will be expanded
and the result padded to achieve the minimum width. If the minimum
field width is positive, the padding will right-align the text.
Negative field width will left-align. The rest of this section
describes various supported tag contents and their expansion.

A simple tag is one where the content is an identifier. When simple
tags are expanded, the named identifier will be looked up in pattern
and the resulting list of values returned, joined together using
comma. For example, to print the family name and style of the
pattern, use the format "%{family} %{style}\n". To extend the family
column to forty characters use "%-40{family}%{style}\n".

Simple tags expand to list of all values for an element. To only
choose one of the values, one can index using the syntax
"%{elt[idx]}". For example, to get the first family name only, use
"%{family[0]}".

If a simple tag ends with "=" and the element is found in the
pattern, the name of the element followed by "=" will be output
before the list of values. For example, "%{weight=}" may expand to
the string "weight=80". Or to the empty string if pattern does not
have weight set.

If a simple tag starts with ":" and the element is found in the
pattern, ":" will be printed first. For example, combining this with
the =, the format "%{:weight=}" may expand to ":weight=80" or to the
empty string if pattern does not have weight set.

If a simple tag contains the string ":-", the rest of the the tag
contents will be used as a default string. The default string is
output if the element is not found in the pattern. For example, the
format "%{:weight=:-123}" may expand to ":weight=80" or to the string
":weight=123" if pattern does not have weight set.

A count tag is one that starts with the character "#" followed by an
element name, and expands to the number of values for the element in
the pattern. For example, "%{#family}" expands to the number of
family names pattern has set, which may be zero.

A sub-expression tag is one that expands a sub-expression. The tag
contents are the sub-expression to expand placed inside another set
of curly braces. Sub-expression tags are useful for aligning an
entire sub-expression, or to apply converters (explained later) to
the entire sub-expression output. For example, the format
"%40{{%{family} %{style}}}" expands the sub-expression to construct
the family name followed by the style, then takes the entire string
and pads it on the left to be at least forty characters.

A filter-out tag is one starting with the character "-" followed by a
comma-separated list of element names, followed by a sub-expression
enclosed in curly braces. The sub-expression will be expanded but
with a pattern that has the listed elements removed from it. For
example, the format "%{-size,pixelsize{sub-expr}}" will expand "sub-
expr" with pattern sans the size and pixelsize elements.

A filter-in tag is one starting with the character "+" followed by a
comma-separated list of element names, followed by a sub-expression
enclosed in curly braces. The sub-expression will be expanded but
with a pattern that only has the listed elements from the surrounding
pattern. For example, the format "%{+family,familylang{sub-expr}}"
will expand "sub-expr" with a sub-pattern consisting only the family
and family lang elements of pattern.

A conditional tag is one starting with the character "?" followed by
a comma-separated list of element conditions, followed by two sub-
expression enclosed in curly braces. An element condition can be an
element name, in which case it tests whether the element is defined
in pattern, or the character "!" followed by an element name, in
which case the test is negated. The conditional passes if all the
element conditions pass. The tag expands the first sub-expression if
the conditional passes, and expands the second sub-expression
otherwise. For example, the format
"%{?size,dpi,!pixelsize{pass}{fail}}" will expand to "pass" if
pattern has size and dpi elements but no pixelsize element, and to
"fail" otherwise.

An enumerate tag is one starting with the string "[]" followed by a
comma-separated list of element names, followed by a sub-expression
enclosed in curly braces. The list of values for the named elements
are walked in parallel and the sub-expression expanded each time with
a pattern just having a single value for those elements, starting
from the first value and continuing as long as any of those elements
has a value. For example, the format
"%{[]family,familylang{%{family} (%{familylang})\n}}" will expand the
pattern "%{family} (%{familylang})\n" with a pattern having only the
first value of the family and familylang elements, then expands it
with the second values, then the third, etc.

As a special case, if an enumerate tag has only one element, and that
element has only one value in the pattern, and that value is of type
FcLangSet, the individual languages in the language set are
enumerated.

A builtin tag is one starting with the character "=" followed by a
builtin name. The following builtins are defined:

unparse
Expands to the result of calling FcNameUnparse() on the
pattern.

fcmatch
Expands to the output of the default output format of the fc-
match command on the pattern, without the final newline.

fclist Expands to the output of the default output format of the fc-
list command on the pattern, without the final newline.

fccat Expands to the output of the default output format of the fc-
cat command on the pattern, without the final newline.

pkgkit Expands to the list of PackageKit font() tags for the pattern.
Currently this includes tags for each family name, and each
language from the pattern, enumerated and sanitized into a set
of tags terminated by newline. Package management systems can
use these tags to tag their packages accordingly.

For example, the format "%{+family,style{%{=unparse}}}\n" will expand
to an unparsed name containing only the family and style element
values from pattern.

The contents of any tag can be followed by a set of zero or more
converters. A converter is specified by the character "|" followed by
the converter name and arguments. The following converters are
defined:

basename
Replaces text with the results of calling FcStrBasename() on
it.

dirname
Replaces text with the results of calling FcStrDirname() on
it.

downcase
Replaces text with the results of calling FcStrDowncase() on
it.

shescape
Escapes text for one level of shell expansion. (Escapes
single-quotes, also encloses text in single-quotes.)

cescape
Escapes text such that it can be used as part of a C string
literal. (Escapes backslash and double-quotes.)

xmlescape
Escapes text such that it can be used in XML and HTML.
(Escapes less-than, greater-than, and ampersand.)

delete(chars)
Deletes all occurrences of each of the characters in chars
from the text. FIXME: This converter is not UTF-8 aware yet.

escape(chars)
Escapes all occurrences of each of the characters in chars by
prepending it by the first character in chars. FIXME: This
converter is not UTF-8 aware yet.

translate(from,to)
Translates all occurrences of each of the characters in from
by replacing them with their corresponding character in to.
If to has fewer characters than from, it will be extended by
repeating its last character. FIXME: This converter is not
UTF-8 aware yet.

For example, the format "%{family|downcase|delete( )}\n" will expand
to the values of the family element in pattern, lower-cased and with
spaces removed.

SINCE

version 2.9.0

Fontconfig 2.15.0 22 12<?> 2023 FcPatternFormat(3)