View source for Gettext MO (Machine Object) file

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From the manpage the gettext program translates a natural language message into the user's language, by looking up the translation in a message catalog.

A Gettext MO file is one of two Gettext file types conveying translations in source code. A Gettext MO file is the second of two files. A first file, a [[Gettext PO (Portable Object) file]], contains strings extracted from the source code for a software application. MO files are generated from PO files. An MO file is a compiled/binary representation of the same data for use by the calling application. 

== Compiling MO files from PO files == 

Given a PO file containing translations, it can be converted to an MO file as follows once <code>gettext</code> is installed locally, e.g. <code>yum install gettext</code>.

The command might look as follows:

* <code>msgfmt messages.po -o messages.mo</code>

== File structure ==

An [https://www.gnu.org/software/gettext/manual/html_node/MO-Files.html excerpt from the documentation] describes the structure of MO files as follows:

 <nowiki>
        byte
             +------------------------------------------+
          0  | magic number = 0x950412de                |
             |                                          |
          4  | file format revision = 0                 |
             |                                          |
          8  | number of strings                        |  == N
             |                                          |
         12  | offset of table with original strings    |  == O
             |                                          |
         16  | offset of table with translation strings |  == T
             |                                          |
         20  | size of hashing table                    |  == S
             |                                          |
         24  | offset of hashing table                  |  == H
             |                                          |
             .                                          .
             .    (possibly more entries later)         .
             .                                          .
             |                                          |
          O  | length & offset 0th string  ----------------.
      O + 8  | length & offset 1st string  ------------------.
              ...                                    ...   | |
O + ((N-1)*8)| length & offset (N-1)th string           |  | |
             |                                          |  | |
          T  | length & offset 0th translation  ---------------.
      T + 8  | length & offset 1st translation  -----------------.
              ...                                    ...   | | | |
T + ((N-1)*8)| length & offset (N-1)th translation      |  | | | |
             |                                          |  | | | |
          H  | start hash table                         |  | | | |
              ...                                    ...   | | | |
  H + S * 4  | end hash table                           |  | | | |
             |                                          |  | | | |
             | NUL terminated 0th string  <----------------' | | |
             |                                          |    | | |
             | NUL terminated 1st string  <------------------' | |
             |                                          |      | |
              ...                                    ...       | |
             |                                          |      | |
             | NUL terminated 0th translation  <---------------' |
             |                                          |        |
             | NUL terminated 1st translation  <-----------------'
             |                                          |
              ...                                    ...
             |                                          |
             +------------------------------------------+
</nowiki>

MO files have the magic number: <code>0x950412de</code>

== Example MO files ==

* [https://github.com/transifex/django-messages/blob/436618b9afe9c8f05a131f79564ab56f09b86a3c/django_messages/locale/ar/LC_MESSAGES/django.mo Arabic MO file for the transifex project]
* [https://github.com/transifex/django-messages/blob/436618b9afe9c8f05a131f79564ab56f09b86a3c/django_messages/locale/de/LC_MESSAGES/django.mo German MO file for the transifex project]

== References == 

* [https://man7.org/linux/man-pages/man1/gettext.1.html Gettext manpage]
* [https://www.gnu.org/software/gettext/manual/html_node/Files.html Gettext files for conveying translations]
* [https://www.gnu.org/software/gettext/manual/html_node/MO-Files.html Gettext MO files]

== Additional links ==

* [https://www.gnu.org/software/gettext/ Gettext project page]
* [https://www.labri.fr/perso/fleury/posts/programming/a-quick-gettext-tutorial.html A Quick Gettext Tutorial]