The g-key-file structure lets you parse, edit or create files containing groups of key-value pairs, which we call key files for lack of a better name. Several freedesktop.org specifications use key files now, e.g. the Desktop Entry Specification and the Icon Theme Specification.

The syntax of key files is described in detail in the Desktop Entry Specification, here is a quick summary: Key files consists of groups of key-value pairs, interspersed with comments.

# this is just an example
# there can be comments before the first group


[First Group]


Name=Key File Example this value shows escaping


# localized strings are stored in multiple key-value pairs
Welcome=Hello
Welcome[de]=Hallo
Welcome[fr_FR]=Bonjour
Welcome[it]=Ciao
Welcome[be@latin]=Hello


[Another Group]


Numbers=2;20;-200;0


Booleans=true;false;true;true  

Lines beginning with a '#' and blank lines are considered comments.

Groups are started by a header line containing the group name enclosed in '[' and ']', and ended implicitly by the start of the next group or the end of the file. Each key-value pair must be contained in a group.

Key-value pairs generally have the form key=value, with the exception of localized strings, which have the form key[locale]=value, with a locale identifier of the form lang_COUNTRYMODIFIER where COUNTRY and MODIFIER are optional. Space before and after the '=' character are ignored. Newline, tab, carriage return and backslash characters in value are escaped as n, t, r, and \, respectively. To preserve leading spaces in values, these can also be escaped as s.

Key files can store strings, possibly with localized variants, integers, booleans and lists of these. Lists are separated by a separator character, typically ';' or ','. To use the list separator character in a value in a list, it has to be escaped by prefixing it with a backslash.

This syntax is obviously inspired by the .ini files commonly met on Windows, but there are some important differences:

• .ini files use the ';' character to begin comments, key files use the '#' character.
• Key files do not allow for ungrouped keys meaning only comments can precede the first group.
• Key files are always encoded in UTF-8.
• Key and Group names are case-sensitive. For example, a group called [GROUP] is a different from [group].
• .ini files do not have a strongly typed boolean entry type, they only have GetProfileInt(). In key files, only true and false (in lower case) are allowed.

Note that in contrast to the Desktop Entry Specification, groups in key files may contain the same key multiple times. The last entry wins. Key files may also contain multiple groups with the same name. They are merged together. Another difference is that keys and group names in key files are not restricted to ASCII characters. Here is an example of loading a key file and reading a value:

(let ((keyfile (g-key-file-new)))
  ;; Load the key file
  (unless (g-key-file-load-from-file keyfile "rtest-glib-key-file.ini" :none)
    (error "Error loading the key file: RTEST-GLIB-KEY-FILE.INI"))
  ;; Read a string from the key file
  (let ((value (g-key-file-string keyfile "First Group" "Welcome")))
    (unless value
      (setf value "default-value"))
    ... ))    

Here is an example of creating and saving a key file:

(let ((keyfile (g-key-file-new)))
  ;; Load existing key file
  (g-key-file-load-from-file keyfile "rtest-glib-key-file.ini" :none)
  ;; Add a string to the First Group
  (setf (g-key-file-string keyfile "First Group" "SomeKey") "New Value")


  ;; Save to a file
  (unless (g-key-file-save-to-file keyfile "rtest-glib-key-file-example.ini")
    (error "Error saving key file."))


  ;; Or save to data for use elsewhere
  (let ((data (g-key-file-to-data keyfile)))
    (unless data
      (error "Error saving key file."))
    ... ))