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While the presentation of gettext focuses mostly on C and
implicitly applies to C++ as well, its scope is far broader than that:
Many programming languages, scripting languages and other textual data
like GUI resources or package descriptions can make use of the gettext
approach.
All programming and scripting languages that have the notion of strings
are eligible to supporting gettext. Supporting gettext
means the following:
gettext would do, but a shorthand
syntax helps keeping the legibility of internationalized programs. For
example, in C we use the syntax _("string"), and in GNU awk we use
the shorthand _"string".
gettext function, or performs equivalent
processing.
ngettext,
dcgettext, dcngettext available from within the language.
These functions are less often used, but are nevertheless necessary for
particular purposes: ngettext for correct plural handling, and
dcgettext and dcngettext for obeying other locale-related
environment variables than LC_MESSAGES, such as LC_TIME or
LC_MONETARY. For these latter functions, you need to make the
LC_* constants, available in the C header <locale.h>,
referenceable from within the language, usually either as enumeration
values or as strings.
textdomain function available from within the
language, or by introducing a magic variable called TEXTDOMAIN.
Similarly, you should allow the programmer to designate where to search
for message catalogs, by providing access to the bindtextdomain
function or — on native Windows platforms — to the wbindtextdomain
function.
setlocale (LC_ALL, "") call during
the startup of your language runtime, or allow the programmer to do so.
Remember that gettext will act as a no-op if the LC_MESSAGES and
LC_CTYPE locale categories are not both set.
xgettext program is being
extended to support very different programming languages. Please
contact the GNU gettext maintainers to help them doing this.
The GNU gettext maintainers will need from you a formal
description of the lexical structure of source files. It should
answer the questions:
Based on this description, the GNU gettext maintainers
can add support to xgettext.
If the string extractor is best integrated into your language's parser,
GNU xgettext can function as a front end to your string extractor.
gettext manual will be extended to
include a pointer to this documentation.
Based on this, the GNU gettext maintainers can add a format string
equivalence checker to msgfmt, so that translators get told
immediately when they have made a mistake during the translation of a
format string.
gettext, but the programs should be portable
across implementations, you should provide a no-i18n emulation, that
makes the other implementations accept programs written for yours,
without actually translating the strings.
gettext maintainers, so they can add support for
your language to ‘po-mode.el’.
On the implementation side, two approaches are possible, with different effects on portability and copyright:
gettext functions if they are found in
the C library. For example, an autoconf test for gettext() and
ngettext() will detect this situation. For the moment, this test
will succeed on GNU systems and on Solaris 11 platforms. No severe
copyright restrictions apply, except if you want to distribute statically
linked binaries.
gettext functionality.
This has the advantage of full portability and no copyright
restrictions, but also the drawback that you have to reimplement the GNU
gettext features (such as the LANGUAGE environment
variable, the locale aliases database, the automatic charset conversion,
and plural handling).
For the programmer, the general procedure is the same as for the C
language. The Emacs PO mode marking supports other languages, and the GNU
xgettext string extractor recognizes other languages based on the
file extension or a command-line option. In some languages,
setlocale is not needed because it is already performed by the
underlying language runtime.
The translator works exactly as in the C language case. The only difference is that when translating format strings, she has to be aware of the language's particular syntax for positional arguments in format strings.
C format strings are described in POSIX (IEEE P1003.1 2001), section XSH 3 fprintf(), http://www.opengroup.org/onlinepubs/007904975/functions/fprintf.html. See also the fprintf() manual page, http://www.linuxvalley.it/encyclopedia/ldp/manpage/man3/printf.3.php, http://informatik.fh-wuerzburg.de/student/i510/man/printf.html.
Although format strings with positions that reorder arguments, such as
"Only %2$d bytes free on '%1$s'." |
which is semantically equivalent to
"'%s' has only %d bytes free." |
are a POSIX/XSI feature and not specified by ISO C 99, translators can rely
on this reordering ability: On the few platforms where printf(),
fprintf() etc. don't support this feature natively, ‘libintl.a’
or ‘libintl.so’ provides replacement functions, and GNU <libintl.h>
activates these replacement functions automatically.
As a special feature for Farsi (Persian) and maybe Arabic, translators can
insert an ‘I’ flag into numeric format directives. For example, the
translation of "%d" can be "%Id". The effect of this flag,
on systems with GNU libc, is that in the output, the ASCII digits are
replaced with the ‘outdigits’ defined in the LC_CTYPE locale
category. On other systems, the gettext function removes this flag,
so that it has no effect.
Note that the programmer should not put this flag into the untranslated string. (Putting the ‘I’ format directive flag into an msgid string would lead to undefined behaviour on platforms without glibc when NLS is disabled.)
Objective C format strings are like C format strings. They support an
additional format directive: "%@", which when executed consumes an argument
of type Object *.
There are two kinds of format strings in Python: those acceptable to
the Python built-in format operator %, labelled as
‘python-format’, and those acceptable to the format method
of the ‘str’ object.
Python % format strings are described in
Python Library reference /
5. Built-in Types /
5.6. Sequence Types /
5.6.2. String Formatting Operations.
https://docs.python.org/2/library/stdtypes.html#string-formatting-operations.
Python brace format strings are described in PEP 3101 – Advanced String Formatting, https://www.python.org/dev/peps/pep-3101/.
There are two kinds of format strings in Java: those acceptable to the
MessageFormat.format function, labelled as ‘java-format’,
and those acceptable to the String.format and
PrintStream.printf functions, labelled as ‘java-printf-format’.
Java format strings are described in the JDK documentation for class
java.text.MessageFormat,
https://docs.oracle.com/javase/7/docs/api/java/text/MessageFormat.html.
See also the ICU documentation
http://icu-project.org/apiref/icu4j/com/ibm/icu/text/MessageFormat.html.
Java printf format strings are described in the JDK documentation
for class java.util.Formatter,
https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html.
C# format strings are described in the .NET documentation for class
System.String and in
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpConFormattingOverview.asp.
Although JavaScript specification itself does not define any format
strings, many JavaScript implementations provide printf-like
functions. xgettext understands a set of common format strings
used in popular JavaScript implementations including Gjs, Seed, and
Node.JS. In such a format string, a directive starts with ‘%’
and is finished by a specifier: ‘%’ denotes a literal percent
sign, ‘c’ denotes a character, ‘s’ denotes a string,
‘b’, ‘d’, ‘o’, ‘x’, ‘X’ denote an integer,
‘f’ denotes floating-point number, ‘j’ denotes a JSON
object.
Scheme format strings are documented in the SLIB manual, section Format Specification.
Lisp format strings are described in the Common Lisp HyperSpec, chapter 22.3 Formatted Output, http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/Body/sec_22-3.html.
Emacs Lisp format strings are documented in the Emacs Lisp reference, section Formatting Strings, https://www.gnu.org/manual/elisp-manual-21-2.8/html_chapter/elisp_4.html#SEC75. Note that as of version 21, XEmacs supports numbered argument specifications in format strings while FSF Emacs doesn't.
librep format strings are documented in the librep manual, section Formatted Output, http://librep.sourceforge.net/librep-manual.html#Formatted%20Output, http://www.gwinnup.org/research/docs/librep.html#SEC122.
Ruby format strings are described in the documentation of the Ruby
functions format and sprintf, in
https://ruby-doc.org/core-2.7.1/Kernel.html#method-i-sprintf.
There are two kinds of format strings in Ruby:
%n$ syntax. Note
that if one argument uses this syntax, all must use this syntax.
%<name>. Note that %{name} is
equivalent to %<name>s.
Shell format strings, as supported by GNU gettext and the ‘envsubst’
program, are strings with references to shell variables in the form
$variable or ${variable}. References of the form
${variable-default},
${variable:-default},
${variable=default},
${variable:=default},
${variable+replacement},
${variable:+replacement},
${variable?ignored},
${variable:?ignored},
that would be valid inside shell scripts, are not supported. The
variable names must consist solely of alphanumeric or underscore
ASCII characters, not start with a digit and be nonempty; otherwise such
a variable reference is ignored.
awk format strings are described in the gawk documentation, section Printf, https://www.gnu.org/manual/gawk/html_node/Printf.html#Printf.
Lua format strings are described in the Lua reference manual, section String Manipulation, https://www.lua.org/manual/5.1/manual.html#pdf-string.format.
Object Pascal format strings are described in the documentation of the Free Pascal runtime library, section Format, https://www.freepascal.org/docs-html/rtl/sysutils/format.html.
Smalltalk format strings are described in the GNU Smalltalk documentation,
class CharArray, methods ‘bindWith:’ and
‘bindWithArguments:’.
https://www.gnu.org/software/smalltalk/gst-manual/gst_68.html#SEC238.
In summary, a directive starts with ‘%’ and is followed by ‘%’
or a nonzero digit (‘1’ to ‘9’).
Qt format strings are described in the documentation of the QString class file:/usr/lib/qt-4.3.0/doc/html/qstring.html. In summary, a directive consists of a ‘%’ followed by a digit. The same directive cannot occur more than once in a format string.
Qt format strings are described in the documentation of the QObject::tr method file:/usr/lib/qt-4.3.0/doc/html/qobject.html. In summary, the only allowed directive is ‘%n’.
KDE 4 format strings are defined as follows: A directive consists of a ‘%’ followed by a non-zero decimal number. If a ‘%n’ occurs in a format strings, all of ‘%1’, ..., ‘%(n-1)’ must occur as well, except possibly one of them.
KUIT (KDE User Interface Text) is compatible with KDE 4 format strings, while it also allows programmers to add semantic information to a format string, through XML markup tags. For example, if the first format directive in a string is a filename, programmers could indicate that with a ‘filename’ tag, like ‘<filename>%1</filename>’.
KUIT format strings are described in https://api.kde.org/frameworks/ki18n/html/prg_guide.html#kuit_markup.
Boost format strings are described in the documentation of the
boost::format class, at
https://www.boost.org/libs/format/doc/format.html.
In summary, a directive has either the same syntax as in a C format string,
such as ‘%1$+5d’, or may be surrounded by vertical bars, such as
‘%|1$+5d|’ or ‘%|1$+5|’, or consists of just an argument number
between percent signs, such as ‘%1%’.
Tcl format strings are described in the ‘format.n’ manual page, http://www.scriptics.com/man/tcl8.3/TclCmd/format.htm.
There are two kinds of format strings in Perl: those acceptable to the
Perl built-in function printf, labelled as ‘perl-format’,
and those acceptable to the libintl-perl function __x,
labelled as ‘perl-brace-format’.
Perl printf format strings are described in the sprintf
section of ‘man perlfunc’.
Perl brace format strings are described in the ‘Locale::TextDomain(3pm)’ manual page of the CPAN package libintl-perl. In brief, Perl format uses placeholders put between braces (‘{’ and ‘}’). The placeholder must have the syntax of simple identifiers.
PHP format strings are described in the documentation of the PHP function
sprintf, in ‘phpdoc/manual/function.sprintf.html’ or
http://www.php.net/manual/en/function.sprintf.php.
These format strings are used inside the GCC sources. In such a format string, a directive starts with ‘%’, is optionally followed by a size specifier ‘l’, an optional flag ‘+’, another optional flag ‘#’, and is finished by a specifier: ‘%’ denotes a literal percent sign, ‘c’ denotes a character, ‘s’ denotes a string, ‘i’ and ‘d’ denote an integer, ‘o’, ‘u’, ‘x’ denote an unsigned integer, ‘.*s’ denotes a string preceded by a width specification, ‘H’ denotes a ‘location_t *’ pointer, ‘D’ denotes a general declaration, ‘F’ denotes a function declaration, ‘T’ denotes a type, ‘A’ denotes a function argument, ‘C’ denotes a tree code, ‘E’ denotes an expression, ‘L’ denotes a programming language, ‘O’ denotes a binary operator, ‘P’ denotes a function parameter, ‘Q’ denotes an assignment operator, ‘V’ denotes a const/volatile qualifier.
These format strings are used inside the GNU Fortran Compiler sources, that is, the Fortran frontend in the GCC sources. In such a format string, a directive starts with ‘%’ and is finished by a specifier: ‘%’ denotes a literal percent sign, ‘C’ denotes the current source location, ‘L’ denotes a source location, ‘c’ denotes a character, ‘s’ denotes a string, ‘i’ and ‘d’ denote an integer, ‘u’ denotes an unsigned integer. ‘i’, ‘d’, and ‘u’ may be preceded by a size specifier ‘l’.
YCP sformat strings are described in the libycp documentation file:/usr/share/doc/packages/libycp/YCP-builtins.html. In summary, a directive starts with ‘%’ and is followed by ‘%’ or a nonzero digit (‘1’ to ‘9’).
For the maintainer, the general procedure differs from the C language case:
XGETTEXT_OPTIONS
variable in ‘po/Makevars’ (see section ‘Makevars’ in ‘po/’) should be adjusted to
match the xgettext options for that particular programming language.
If the package uses more than one programming language with gettext
support, it becomes necessary to change the POT file construction rule
in ‘po/Makefile.in.in’. It is recommended to make one xgettext
invocation per programming language, each with the options appropriate for
that language, and to combine the resulting files using msgcat.
gcc, gpp, gobjc, glibc, gettext
gcc, g++, gobjc, libc6-dev, libasprintf-dev
For C: c, h.
For C++: C, c++, cc, cxx, cpp, hpp.
For Objective C: m.
"abc"
_("abc")
gettext, dgettext, dcgettext, ngettext,
dngettext, dcngettext
textdomain function
bindtextdomain and wbindtextdomain functions
Programmer must call setlocale (LC_ALL, "")
#include <libintl.h>
#include <locale.h>
#define _(string) gettext (string)
Use
xgettext -k_
fprintf "%2$d %1$d"
In C++: autosprintf "%2$d %1$d"
(see (autosprintf)Top section `Introduction' in GNU autosprintf)
autoconf (gettext.m4) and #if ENABLE_NLS
yes
The following examples are available in the ‘examples’ directory:
hello-c, hello-c-gnome, hello-c++, hello-c++-qt,
hello-c++-kde, hello-c++-gnome, hello-c++-wxwidgets,
hello-objc, hello-objc-gnustep, hello-objc-gnome.
python
python
py
'abc', u'abc', r'abc', ur'abc',
"abc", u"abc", r"abc", ur"abc",
'''abc''', u'''abc''', r'''abc''', ur'''abc''',
"""abc""", u"""abc""", r"""abc""", ur"""abc"""
_('abc') etc.
gettext.gettext, gettext.dgettext,
gettext.ngettext, gettext.dngettext,
also ugettext, ungettext
gettext.textdomain function, or
gettext.install(domain) function
gettext.bindtextdomain function, or
gettext.install(domain,localedir) function
not used by the gettext emulation
import gettext
emulate
xgettext
'...%(ident)d...' % { 'ident': value }
fully portable
—
An example is available in the ‘examples’ directory: hello-python.
A note about format strings: Python supports format strings with unnamed
arguments, such as '...%d...', and format strings with named arguments,
such as '...%(ident)d...'. The latter are preferable for
internationalized programs, for two reasons:
"'%(volume)s' has only %(freespace)d bytes free." |
to
"Only %(freespace)d bytes free on '%(volume)s'." |
Additionally, the identifiers also provide some context to the translator.
"one hour" instead of "1 hour". Omitting
individual arguments from format strings like this is only possible with
the named argument syntax. (With unnamed arguments, Python – unlike C –
verifies that the format string uses all supplied arguments.)
java, java2
default-jdk
java
"abc", """text block"""
i18n("abc")
GettextResource.gettext, GettextResource.ngettext,
GettextResource.pgettext, GettextResource.npgettext
—, use ResourceBundle.getResource instead
—, use CLASSPATH instead
automatic
—
—, uses a Java specific message catalog format
xgettext -ki18n
MessageFormat.format "{1,number} {0,number}"
or String.format "%2$d %1$d"
fully portable
—
Before marking strings as internationalizable, uses of the string
concatenation operator need to be converted to MessageFormat
applications. For example, "file "+filename+" not found" becomes
MessageFormat.format("file {0} not found", new Object[] { filename }).
Only after this is done, can the strings be marked and extracted.
GNU gettext uses the native Java internationalization mechanism, namely
ResourceBundles. There are two formats of ResourceBundles:
.properties files and .class files. The .properties
format is a text file which the translators can directly edit, like PO
files, but which doesn't support plural forms. Whereas the .class
format is compiled from .java source code and can support plural
forms (provided it is accessed through an appropriate API, see below).
To convert a PO file to a .properties file, the msgcat
program can be used with the option --properties-output. To convert
a .properties file back to a PO file, the msgcat program
can be used with the option --properties-input. All the tools
that manipulate PO files can work with .properties files as well,
if given the --properties-input and/or --properties-output
option.
To convert a PO file to a ResourceBundle class, the msgfmt program
can be used with the option --java or --java2. To convert a
ResourceBundle back to a PO file, the msgunfmt program can be used
with the option --java.
Two different programmatic APIs can be used to access ResourceBundles.
Note that both APIs work with all kinds of ResourceBundles, whether
GNU gettext generated classes, or other .class or .properties
files.
java.util.ResourceBundle API.
In particular, its getString function returns a string translation.
Note that a missing translation yields a MissingResourceException.
This has the advantage of being the standard API. And it does not require
any additional libraries, only the msgcat generated .properties
files or the msgfmt generated .class files. But it cannot do
plural handling, even if the resource was generated by msgfmt from
a PO file with plural handling.
gnu.gettext.GettextResource API.
Reference documentation in Javadoc 1.1 style format is in the javadoc2 directory.
Its gettext function returns a string translation. Note that when
a translation is missing, the msgid argument is returned unchanged.
This has the advantage of having the ngettext function for plural
handling and the pgettext and npgettext for strings constraint
to a particular context.
To use this API, one needs the libintl.jar file which is part of
the GNU gettext package and distributed under the LGPL.
Four examples, using the second API, are available in the ‘examples’
directory: hello-java, hello-java-awt, hello-java-swing,
hello-java-qtjambi.
Now, to make use of the API and define a shorthand for ‘getString’, there are three idioms that you can choose from:
ResourceBundle instance and the shorthand:
private static ResourceBundle myResources =
ResourceBundle.getBundle("domain-name");
public static String i18n(String s) {
return myResources.getString(s);
}
|
All classes containing internationalized strings then contain
import static Util.i18n; |
and the shorthand is used like this:
System.out.println(i18n("Operation completed."));
|
ResourceBundle instance:
public static ResourceBundle myResources =
ResourceBundle.getBundle("domain-name");
|
All classes containing internationalized strings then contain
private static ResourceBundle res = Util.myResources;
private static String i18n(String s) { return res.getString(s); }
|
and the shorthand is used like this:
System.out.println(i18n("Operation completed."));
|
public class S {
public static ResourceBundle myResources =
ResourceBundle.getBundle("domain-name");
public static String i18n(String s) {
return myResources.getString(s);
}
}
|
and the shorthand is used like this:
System.out.println(S.i18n("Operation completed."));
|
Which of the three idioms you choose, will depend on whether your project requires portability to Java versions prior to Java 1.5 and, if so, whether copying two lines of codes into every class is more acceptable in your project than a class with a single-letter name.
mono
mono-mcs
cs
"abc", @"abc"
_("abc")
GettextResourceManager.GetString,
GettextResourceManager.GetPluralString
GettextResourceManager.GetParticularString
GettextResourceManager.GetParticularPluralString
new GettextResourceManager(domain)
—, compiled message catalogs are located in subdirectories of the directory containing the executable
automatic
—
—, uses a C# specific message catalog format
xgettext -k_
String.Format "{1} {0}"
fully portable
—
Before marking strings as internationalizable, uses of the string
concatenation operator need to be converted to String.Format
invocations. For example, "file "+filename+" not found" becomes
String.Format("file {0} not found", filename).
Only after this is done, can the strings be marked and extracted.
GNU gettext uses the native C#/.NET internationalization mechanism, namely
the classes ResourceManager and ResourceSet. Applications
use the ResourceManager methods to retrieve the native language
translation of strings. An instance of ResourceSet is the in-memory
representation of a message catalog file. The ResourceManager loads
and accesses ResourceSet instances as needed to look up the
translations.
There are two formats of ResourceSets that can be directly loaded by
the C# runtime: .resources files and .dll files.
.resources format is a binary file usually generated through the
resgen or monoresgen utility, but which doesn't support plural
forms. .resources files can also be embedded in .NET .exe files.
This only affects whether a file system access is performed to load the message
catalog; it doesn't affect the contents of the message catalog.
.dll format is a binary file that is compiled
from .cs source code and can support plural forms (provided it is
accessed through the GNU gettext API, see below).
Note that these .NET .dll and .exe files are not tied to a
particular platform; their file format and GNU gettext for C# can be used
on any platform.
To convert a PO file to a .resources file, the msgfmt program
can be used with the option ‘--csharp-resources’. To convert a
.resources file back to a PO file, the msgunfmt program can be
used with the option ‘--csharp-resources’. You can also, in some cases,
use the monoresgen program (from the mono/mcs package).
This program can also convert a .resources file back to a PO file. But
beware: as of this writing (January 2004), the monoresgen converter is
quite buggy.
To convert a PO file to a .dll file, the msgfmt program can be
used with the option --csharp. The result will be a .dll file
containing a subclass of GettextResourceSet, which itself is a subclass
of ResourceSet. To convert a .dll file containing a
GettextResourceSet subclass back to a PO file, the msgunfmt
program can be used with the option --csharp.
The advantages of the .dll format over the .resources format
are:
ResourceManager constructor provided by the system, the set of
.resources files for an application must be specified when the
application is built and cannot be extended afterwards.
.dll format supports the plural
handling function GetPluralString. Whereas .resources files can
only contain data and only support lookups that depend on a single string.
.dll format supports the
query-with-context functions GetParticularString and
GetParticularPluralString. Whereas .resources files can
only contain data and only support lookups that depend on a single string.
GettextResourceManager that loads the message catalogs in
.dll format also provides for inheritance on a per-message basis.
For example, in Austrian (de_AT) locale, translations from the German
(de) message catalog will be used for messages not found in the
Austrian message catalog. This has the consequence that the Austrian
translators need only translate those few messages for which the translation
into Austrian differs from the German one. Whereas when working with
.resources files, each message catalog must provide the translations
of all messages by itself.
GettextResourceManager that loads the message catalogs in
.dll format also provides for a fallback: The English msgid is
returned when no translation can be found. Whereas when working with
.resources files, a language-neutral .resources file must
explicitly be provided as a fallback.
On the side of the programmatic APIs, the programmer can use either the
standard ResourceManager API and the GNU GettextResourceManager
API. The latter is an extension of the former, because
GettextResourceManager is a subclass of ResourceManager.
System.Resources.ResourceManager API.
This API works with resources in .resources format.
The creation of the ResourceManager is done through
new ResourceManager(domainname, Assembly.GetExecutingAssembly()) |
The GetString function returns a string's translation. Note that this
function returns null when a translation is missing (i.e. not even found in
the fallback resource file).
GNU.Gettext.GettextResourceManager API.
This API works with resources in .dll format.
Reference documentation is in the csharpdoc directory.
The creation of the ResourceManager is done through
new GettextResourceManager(domainname) |
The GetString function returns a string's translation. Note that when
a translation is missing, the msgid argument is returned unchanged.
The GetPluralString function returns a string translation with plural
handling, like the ngettext function in C.
The GetParticularString function returns a string's translation,
specific to a particular context, like the pgettext function in C.
Note that when a translation is missing, the msgid argument is returned
unchanged.
The GetParticularPluralString function returns a string translation,
specific to a particular context, with plural handling, like the
npgettext function in C.
To use this API, one needs the GNU.Gettext.dll file which is part of
the GNU gettext package and distributed under the LGPL.
You can also mix both approaches: use the
GNU.Gettext.GettextResourceManager constructor, but otherwise use
only the ResourceManager type and only the GetString method.
This is appropriate when you want to profit from the tools for PO files,
but don't want to change an existing source code that uses
ResourceManager and don't (yet) need the GetPluralString method.
Two examples, using the second API, are available in the ‘examples’
directory: hello-csharp, hello-csharp-forms.
Now, to make use of the API and define a shorthand for ‘GetString’, there are two idioms that you can choose from:
ResourceManager instance:
public static GettextResourceManager MyResourceManager =
new GettextResourceManager("domain-name");
|
All classes containing internationalized strings then contain
private static GettextResourceManager Res = Util.MyResourceManager;
private static String _(String s) { return Res.GetString(s); }
|
and the shorthand is used like this:
Console.WriteLine(_("Operation completed."));
|
public class S {
public static GettextResourceManager MyResourceManager =
new GettextResourceManager("domain-name");
public static String _(String s) {
return MyResourceManager.GetString(s);
}
}
|
and the shorthand is used like this:
Console.WriteLine(S._("Operation completed."));
|
Which of the two idioms you choose, will depend on whether copying two lines of codes into every class is more acceptable in your project than a class with a single-letter name.
js
gjs
js
"abc"
'abc'
`abc`
_("abc")
gettext, dgettext, dcgettext, ngettext,
dngettext
textdomain function
bindtextdomain function
automatic
—
use, or emulate
xgettext
—
On platforms without gettext, the functions are not available.
—
guile
guile-2.0
scm
"abc"
(_ "abc"), _"abc" (GIMP script-fu extension)
gettext, ngettext
textdomain
bindtextdomain
(catch #t (lambda () (setlocale LC_ALL "")) (lambda args #f))
(use-modules (ice-9 format))
use
xgettext -k_
—
On platforms without gettext, no translation.
—
An example is available in the ‘examples’ directory: hello-guile.
clisp 2.28 or newer
clisp
lisp
"abc"
(_ "abc"), (ENGLISH "abc")
i18n:gettext, i18n:ngettext
i18n:textdomain
i18n:textdomaindir
automatic
—
use
xgettext -k_ -kENGLISH
format "~1@*~D ~0@*~D"
On platforms without gettext, no translation.
—
An example is available in the ‘examples’ directory: hello-clisp.
clisp
clisp
d
"abc"
ENGLISH ? "abc" : ""
GETTEXT("abc")
GETTEXTL("abc")
clgettext, clgettextl
—
—
automatic
#include "lispbibl.c"
use
clisp-xgettext
fprintf "%2$d %1$d"
On platforms without gettext, no translation.
—
emacs, xemacs
emacs, xemacs21
el
"abc"
(_"abc")
gettext, dgettext (xemacs only)
domain special form (xemacs only)
bind-text-domain function (xemacs only)
automatic
—
use
xgettext
format "%2$d %1$d"
Only XEmacs. Without I18N3 defined at build time, no translation.
—
librep 0.15.3 or newer
librep16
jl
"abc"
(_"abc")
gettext
textdomain function
bindtextdomain function
—
(require 'rep.i18n.gettext)
use
xgettext
format "%2$d %1$d"
On platforms without gettext, no translation.
—
An example is available in the ‘examples’ directory: hello-librep.
ruby, ruby-gettext
ruby, ruby-gettext
rb
"abc", 'abc', %q/abc/ etc.,
%q(abc), %q[abc], %q{abc}
_("abc")
gettext, ngettext
—
bindtextdomain function
—
require 'gettext'
include GetText
emulate
xgettext
sprintf("%2$d %1$d", x, y)
"%{new} replaces %{old}" % {:old => oldvalue, :new => newvalue}
fully portable
—
bash, gettext
bash, gettext-base
sh
"abc", 'abc', abc
"`gettext \"abc\"`"
gettext, ngettext programs
eval_gettext, eval_ngettext, eval_pgettext,
eval_npgettext shell functions
environment variable TEXTDOMAIN
environment variable TEXTDOMAINDIR
automatic
. gettext.sh
use
xgettext
—
fully portable
—
An example is available in the ‘examples’ directory: hello-sh.
Preparing a shell script for internationalization is conceptually similar to the steps described in Preparing Program Sources. The concrete steps for shell scripts are as follows.
. gettext.sh |
near the top of the script. gettext.sh is a shell function library
that provides the functions
eval_gettext (see Invoking the eval_gettext function),
eval_ngettext (see Invoking the eval_ngettext function),
eval_pgettext (see Invoking the eval_pgettext function), and
eval_npgettext (see Invoking the eval_npgettext function).
You have to ensure that gettext.sh can be found in the PATH.
TEXTDOMAIN and TEXTDOMAINDIR environment
variables. Usually TEXTDOMAIN is the package or program name, and
TEXTDOMAINDIR is the absolute pathname corresponding to
$prefix/share/locale, where $prefix is the installation location.
TEXTDOMAIN=@PACKAGE@ export TEXTDOMAIN TEXTDOMAINDIR=@LOCALEDIR@ export TEXTDOMAINDIR |
"`...`" or "$(...)"), variable access with defaulting (like
${variable-default}), access to positional arguments
(like $0, $1, ...) or highly volatile shell variables (like
$?). This can always be done through simple local code restructuring.
For example,
echo "Usage: $0 [OPTION] FILE..." |
becomes
program_name=$0 echo "Usage: $program_name [OPTION] FILE..." |
Similarly,
echo "Remaining files: `ls | wc -l`" |
becomes
filecount="`ls | wc -l`" echo "Remaining files: $filecount" |
When doing this, you also need to add an extra backslash before the dollar sign in references to shell variables, so that the ‘eval_gettext’ function receives the translatable string before the variable values are substituted into it. For example,
echo "Remaining files: $filecount" |
becomes
eval_gettext "Remaining files: \$filecount"; echo |
If the output command is not ‘echo’, you can make it use ‘echo’ nevertheless, through the use of backquotes. However, note that inside backquotes, backslashes must be doubled to be effective (because the backquoting eats one level of backslashes). For example, assuming that ‘error’ is a shell function that signals an error,
error "file not found: $filename" |
is first transformed into
error "`echo \"file not found: \$filename\"`" |
which then becomes
error "`eval_gettext \"file not found: \\\$filename\"`" |
gettext.sh gettext.sh, contained in the run-time package of GNU gettext, provides
the following:
echo is set to a command that outputs its first argument
and a newline, without interpreting backslashes in the argument string.
eval_gettext function.
eval_ngettext function.
eval_pgettext function.
eval_npgettext function.
gettext program gettext [option] [[textdomain] msgid] gettext [option] -s [msgid]... |
The gettext program displays the native language translation of a
textual message.
Arguments
Specify the context for the messages to be translated. See Using contexts for solving ambiguities for details.
Retrieve translated messages from textdomain. Usually a textdomain corresponds to a package, a program, or a module of a program.
Enable expansion of some escape sequences. This option is for compatibility with the ‘echo’ program or shell built-in. The escape sequences ‘\a’, ‘\b’, ‘\c’, ‘\f’, ‘\n’, ‘\r’, ‘\t’, ‘\v’, ‘\\’, and ‘\’ followed by one to three octal digits, are interpreted like the System V ‘echo’ program did.
This option is only for compatibility with the ‘echo’ program or shell built-in. It has no effect.
Display this help and exit.
This option has only an effect if the -s option is given. It
suppresses the additional newline at the end.
Output version information and exit.
Retrieve translated message corresponding to msgid from textdomain.
If the textdomain parameter is not given, the domain is determined from
the environment variable TEXTDOMAIN. If the message catalog is not
found in the regular directory, another location can be specified with the
environment variable TEXTDOMAINDIR.
When used with the -s option the program behaves like the ‘echo’
command. But it does not simply copy its arguments to stdout. Instead those
messages found in the selected catalog are translated. Also, a newline is
added at the end, unless either the option -n is specified or the
option -e is specified and some of the argument strings contains a
‘\c’ escape sequence.
Note: xgettext supports only the one-argument form of the
gettext invocation, where no options are present and the
textdomain is implicit, from the environment.
ngettext program ngettext [option] [textdomain] msgid msgid-plural count |
The ngettext program displays the native language translation of a
textual message whose grammatical form depends on a number.
Arguments
Specify the context for the messages to be translated. See Using contexts for solving ambiguities for details.
Retrieve translated messages from textdomain. Usually a textdomain corresponds to a package, a program, or a module of a program.
Enable expansion of some escape sequences. This option is for compatibility with the ‘gettext’ program. The escape sequences ‘\a’, ‘\b’, ‘\f’, ‘\n’, ‘\r’, ‘\t’, ‘\v’, ‘\\’, and ‘\’ followed by one to three octal digits, are interpreted like the System V ‘echo’ program did.
This option is only for compatibility with the ‘gettext’ program. It has no effect.
Display this help and exit.
Output version information and exit.
Retrieve translated message from textdomain.
Translate msgid (English singular) / msgid-plural (English plural).
Choose singular/plural form based on this value.
If the textdomain parameter is not given, the domain is determined from
the environment variable TEXTDOMAIN. If the message catalog is not
found in the regular directory, another location can be specified with the
environment variable TEXTDOMAINDIR.
Note: xgettext supports only the three-arguments form of the
ngettext invocation, where no options are present and the
textdomain is implicit, from the environment.
envsubst program envsubst [option] [shell-format] |
The envsubst program substitutes the values of environment variables.
Operation mode
Output the variables occurring in shell-format.
Informative output
Display this help and exit.
Output version information and exit.
In normal operation mode, standard input is copied to standard output,
with references to environment variables of the form $VARIABLE or
${VARIABLE} being replaced with the corresponding values. If a
shell-format is given, only those environment variables that are
referenced in shell-format are substituted; otherwise all environment
variables references occurring in standard input are substituted.
These substitutions are a subset of the substitutions that a shell performs
on unquoted and double-quoted strings. Other kinds of substitutions done
by a shell, such as ${variable-default} or
$(command-list) or `command-list`, are not performed
by the envsubst program, due to security reasons.
When --variables is used, standard input is ignored, and the output
consists of the environment variables that are referenced in
shell-format, one per line.
eval_gettext function eval_gettext msgid |
This function outputs the native language translation of a textual message, performing dollar-substitution on the result. Note that only shell variables mentioned in msgid will be dollar-substituted in the result.
eval_ngettext function eval_ngettext msgid msgid-plural count |
This function outputs the native language translation of a textual message whose grammatical form depends on a number, performing dollar-substitution on the result. Note that only shell variables mentioned in msgid or msgid-plural will be dollar-substituted in the result.
eval_pgettext function eval_pgettext msgctxt msgid |
This function outputs the native language translation of a textual message in the given context msgctxt (see Using contexts for solving ambiguities), performing dollar-substitution on the result. Note that only shell variables mentioned in msgid will be dollar-substituted in the result.
eval_npgettext function eval_npgettext msgctxt msgid msgid-plural count |
This function outputs the native language translation of a textual message whose grammatical form depends on a number in the given context msgctxt (see Using contexts for solving ambiguities), performing dollar-substitution on the result. Note that only shell variables mentioned in msgid or msgid-plural will be dollar-substituted in the result.
GNU bash 2.0 or newer has a special shorthand for translating a
string and substituting variable values in it: $"msgid". But
the use of this construct is discouraged, due to the security
holes it opens and due to its portability problems.
The security holes of $"..." come from the fact that after looking up
the translation of the string, bash processes it like it processes
any double-quoted string: dollar and backquote processing, like ‘eval’
does.
0x60. For example, the byte sequence \xe0\x60 is a single
character in these locales. Many versions of bash (all versions
up to bash-2.05, and newer versions on platforms without mbsrtowcs()
function) don't know about character boundaries and see a backquote character
where there is only a particular Chinese character. Thus it can start
executing part of the translation as a command list. This situation can occur
even without the translator being aware of it: if the translator provides
translations in the UTF-8 encoding, it is the gettext() function which
will, during its conversion from the translator's encoding to the user's
locale's encoding, produce the dangerous \x60 bytes.
"`...`" or dollar-parentheses "$(...)" in her translations.
The enclosed strings would be executed as command lists by the shell.
The portability problem is that bash must be built with
internationalization support; this is normally not the case on systems
that don't have the gettext() function in libc.
gawk 3.1 or newer
gawk
awk, gawk, twjr.
The file extension twjr is used by TexiWeb Jr
(https://github.com/arnoldrobbins/texiwebjr).
"abc"
_"abc"
dcgettext, missing dcngettext in gawk-3.1.0
TEXTDOMAIN variable
bindtextdomain function
automatic, but missing setlocale (LC_MESSAGES, "") in gawk-3.1.0
—
use
xgettext
printf "%2$d %1$d" (GNU awk only)
On platforms without gettext, no translation. On non-GNU awks, you must
define dcgettext, dcngettext and bindtextdomain
yourself.
—
An example is available in the ‘examples’ directory: hello-gawk.
lua
lua, lua-gettext
You need to install the lua-gettext package from
https://gitlab.com/sukhichev/lua-gettext/blob/master/README.us.md.
Debian and Ubuntu packages of it are available. Download the
appropriate one, and install it through
‘sudo dpkg -i lua-gettext_0.0_amd64.deb’.
lua
"abc"
'abc'
[[abc]]
[=[abc]=]
[==[abc]==]
_("abc")
gettext.gettext, gettext.dgettext, gettext.dcgettext,
gettext.ngettext, gettext.dngettext, gettext.dcngettext
textdomain function
bindtextdomain function
automatic
require 'gettext' or running lua interpreter with -l gettext option
use
xgettext
—
On platforms without gettext, the functions are not available.
—
fpk
fp-compiler, fp-units-fcl
pp, pas
'abc'
automatic
—, use ResourceString data type instead
—, use TranslateResourceStrings function instead
—, use TranslateResourceStrings function instead
automatic, but uses only LANG, not LC_MESSAGES or LC_ALL
{$mode delphi} or {$mode objfpc}uses gettext;
emulate partially
ppc386 followed by xgettext or rstconv
uses sysutils;format "%1:d %0:d"
?
—
The Pascal compiler has special support for the ResourceString data
type. It generates a .rst file. This is then converted to a
.pot file by use of xgettext or rstconv. At runtime,
a .mo file corresponding to translations of this .pot file
can be loaded using the TranslateResourceStrings function in the
gettext unit.
An example is available in the ‘examples’ directory: hello-pascal.
smalltalk
gnu-smalltalk
st
'abc'
NLS ? 'abc'
LcMessagesDomain>>#at:, LcMessagesDomain>>#at:plural:with:
LcMessages>>#domain:localeDirectory: (returns a LcMessagesDomain
object).
Example: I18N Locale default messages domain: 'gettext' localeDirectory: /usr/local/share/locale'
LcMessages>>#domain:localeDirectory:, see above.
Automatic if you use I18N Locale default.
PackageLoader fileInPackage: 'I18N'!
emulate
xgettext
'%1 %2' bindWith: 'Hello' with: 'world'
fully portable
—
An example is available in the ‘examples’ directory:
hello-smalltalk.
vala
valac
vala
"abc"
"""abc"""
_("abc")
gettext, dgettext, dcgettext, ngettext,
dngettext, dpgettext, dpgettext2
textdomain function, defined under the Intl namespace
bindtextdomain function, defined under the Intl namespace
Programmer must call Intl.setlocale (LocaleCategory.ALL, "")
—
Use
xgettext
Same as for the C language.
autoconf (gettext.m4) and #if ENABLE_NLS
yes
wxGTK, gettext
libwxgtk3.0-dev
cpp
"abc"
_("abc")
wxLocale::GetString, wxGetTranslation
wxLocale::AddCatalog
wxLocale::AddCatalogLookupPathPrefix
wxLocale::Init, wxSetLocale
#include <wx/intl.h>
emulate, see include/wx/intl.h and src/common/intl.cpp
xgettext
wxString::Format supports positions if and only if the system has
wprintf(), vswprintf() functions and they support positions
according to POSIX.
fully portable
yes
tcl
tcl
tcl
"abc"
[_ "abc"]
::msgcat::mc
—
—, use ::msgcat::mcload instead
automatic, uses LANG, but ignores LC_MESSAGES and LC_ALL
package require msgcat
proc _ {s} {return [::msgcat::mc $s]}
—, uses a Tcl specific message catalog format
xgettext -k_
format "%2\$d %1\$d"
fully portable
—
Two examples are available in the ‘examples’ directory:
hello-tcl, hello-tcl-tk.
Before marking strings as internationalizable, substitutions of variables
into the string need to be converted to format applications. For
example, "file $filename not found" becomes
[format "file %s not found" $filename].
Only after this is done, can the strings be marked and extracted.
After marking, this example becomes
[format [_ "file %s not found"] $filename] or
[msgcat::mc "file %s not found" $filename]. Note that the
msgcat::mc function implicitly calls format when more than one
argument is given.
perl
perl, libintl-perl
pl, PL, pm, perl, cgi
"abc"
'abc'
qq (abc)
q (abc)
qr /abc/
qx (/bin/date)
/pattern match/
?pattern match?
s/substitution/operators/
$tied_hash{"message"}
$tied_hash_reference->{"message"}
__ (double underscore)
gettext, dgettext, dcgettext, ngettext,
dngettext, dcngettext, pgettext, dpgettext,
dcpgettext, npgettext, dnpgettext,
dcnpgettext
textdomain function
bindtextdomain function
bind_textdomain_codeset function
Use setlocale (LC_ALL, "");
use POSIX;
use Locale::TextDomain; (included in the package libintl-perl
which is available on the Comprehensive Perl Archive Network CPAN,
https://www.cpan.org/).
platform dependent: gettext_pp emulates, gettext_xs uses GNU gettext
xgettext -k__ -k\$__ -k%__ -k__x -k__n:1,2 -k__nx:1,2 -k__xn:1,2
-kN__ -kN__n:1,2 -k__p:1c,2 -k__np:1c,2,3 -kN__p:1c,2 -kN__np:1c,2,3
Both kinds of format strings support formatting with positions.
printf "%2\$d %1\$d", ... (requires Perl 5.8.0 or newer)
__expand("[new] replaces [old]", old => $oldvalue, new => $newvalue)
The libintl-perl package is platform independent but is not
part of the Perl core. The programmer is responsible for
providing a dummy implementation of the required functions if the
package is not installed on the target system.
—
Included in libintl-perl, available on CPAN
(https://www.cpan.org/).
An example is available in the ‘examples’ directory: hello-perl.
The xgettext parser backend for Perl differs significantly from
the parser backends for other programming languages, just as Perl
itself differs significantly from other programming languages. The
Perl parser backend offers many more string marking facilities than
the other backends but it also has some Perl specific limitations, the
worst probably being its imperfectness.
It is often heard that only Perl can parse Perl. This is not true. Perl cannot be parsed at all, it can only be executed. Perl has various built-in ambiguities that can only be resolved at runtime.
The following example may illustrate one common problem:
print gettext "Hello World!"; |
Although this example looks like a bullet-proof case of a function invocation, it is not:
open gettext, ">testfile" or die; print gettext "Hello world!" |
In this context, the string gettext looks more like a
file handle. But not necessarily:
use Locale::Messages qw (:libintl_h); open gettext ">testfile" or die; print gettext "Hello world!"; |
Now, the file is probably syntactically incorrect, provided that the module
Locale::Messages found first in the Perl include path exports a
function gettext. But what if the module
Locale::Messages really looks like this?
use vars qw (*gettext); 1; |
In this case, the string gettext will be interpreted as a file
handle again, and the above example will create a file ‘testfile’
and write the string “Hello world!” into it. Even advanced
control flow analysis will not really help:
if (0.5 < rand) {
eval "use Sane";
} else {
eval "use InSane";
}
print gettext "Hello world!";
|
If the module Sane exports a function gettext that does
what we expect, and the module InSane opens a file for writing
and associates the handle gettext with this output
stream, we are clueless again about what will happen at runtime. It is
completely unpredictable. The truth is that Perl has so many ways to
fill its symbol table at runtime that it is impossible to interpret a
particular piece of code without executing it.
Of course, xgettext will not execute your Perl sources while
scanning for translatable strings, but rather use heuristics in order
to guess what you meant.
Another problem is the ambiguity of the slash and the question mark. Their interpretation depends on the context:
# A pattern match. print "OK\n" if /foobar/; # A division. print 1 / 2; # Another pattern match. print "OK\n" if ?foobar?; # Conditional. print $x ? "foo" : "bar"; |
The slash may either act as the division operator or introduce a
pattern match, whereas the question mark may act as the ternary
conditional operator or as a pattern match, too. Other programming
languages like awk present similar problems, but the consequences of a
misinterpretation are particularly nasty with Perl sources. In awk
for instance, a statement can never exceed one line and the parser
can recover from a parsing error at the next newline and interpret
the rest of the input stream correctly. Perl is different, as a
pattern match is terminated by the next appearance of the delimiter
(the slash or the question mark) in the input stream, regardless of
the semantic context. If a slash is really a division sign but
mis-interpreted as a pattern match, the rest of the input file is most
probably parsed incorrectly.
There are certain cases, where the ambiguity cannot be resolved at all:
$x = wantarray ? 1 : 0; |
The Perl built-in function wantarray does not accept any arguments.
The Perl parser therefore knows that the question mark does not start
a regular expression but is the ternary conditional operator.
sub wantarrays {}
$x = wantarrays ? 1 : 0;
|
Now the situation is different. The function wantarrays takes
a variable number of arguments (like any non-prototyped Perl function).
The question mark is now the delimiter of a pattern match, and hence
the piece of code does not compile.
sub wantarrays() {}
$x = wantarrays ? 1 : 0;
|
Now the function is prototyped, Perl knows that it does not accept any
arguments, and the question mark is therefore interpreted as the
ternaray operator again. But that unfortunately outsmarts xgettext.
The Perl parser in xgettext cannot know whether a function has
a prototype and what that prototype would look like. It therefore makes
an educated guess. If a function is known to be a Perl built-in and
this function does not accept any arguments, a following question mark
or slash is treated as an operator, otherwise as the delimiter of a
following regular expression. The Perl built-ins that do not accept
arguments are wantarray, fork, time, times,
getlogin, getppid, getpwent, getgrent,
gethostent, getnetent, getprotoent, getservent,
setpwent, setgrent, endpwent, endgrent,
endhostent, endnetent, endprotoent, and
endservent.
If you find that xgettext fails to extract strings from
portions of your sources, you should therefore look out for slashes
and/or question marks preceding these sections. You may have come
across a bug in xgettext's Perl parser (and of course you
should report that bug). In the meantime you should consider to
reformulate your code in a manner less challenging to xgettext.
In particular, if the parser is too dumb to see that a function does not accept arguments, use parentheses:
$x = somefunc() ? 1 : 0; $y = (somefunc) ? 1 : 0; |
In fact the Perl parser itself has similar problems and warns you about such constructs.
Unless you instruct xgettext otherwise by invoking it with one
of the options --keyword or -k, it will recognize the
following keywords in your Perl sources:
gettext
dgettext:2
The second argument will be extracted.
dcgettext:2
The second argument will be extracted.
ngettext:1,2
The first (singular) and the second (plural) argument will be extracted.
dngettext:2,3
The second (singular) and the third (plural) argument will be extracted.
dcngettext:2,3
The second (singular) and the third (plural) argument will be extracted.
pgettext:1c,2
The first (message context) and the second argument will be extracted.
dpgettext:2c,3
The second (message context) and the third argument will be extracted.
dcpgettext:2c,3
The second (message context) and the third argument will be extracted.
npgettext:1c,2,3
The first (message context), second (singular), and third (plural) argument will be extracted.
dnpgettext:2c,3,4
The second (message context), third (singular), and fourth (plural) argument will be extracted.
dcnpgettext:2c,3,4
The second (message context), third (singular), and fourth (plural) argument will be extracted.
gettext_noop
%gettext
The keys of lookups into the hash %gettext will be extracted.
$gettext
The keys of lookups into the hash reference $gettext will be extracted.
Translating messages at runtime is normally performed by looking up the
original string in the translation database and returning the
translated version. The “natural” Perl implementation is a hash
lookup, and, of course, xgettext supports such practice.
print __"Hello world!";
print $__{"Hello world!"};
print $__->{"Hello world!"};
print $$__{"Hello world!"};
|
The above four lines all do the same thing. The Perl module
Locale::TextDomain exports by default a hash %__ that
is tied to the function __(). It also exports a reference
$__ to %__.
If an argument to the xgettext option --keyword,
resp. -k starts with a percent sign, the rest of the keyword is
interpreted as the name of a hash. If it starts with a dollar
sign, the rest of the keyword is interpreted as a reference to a
hash.
Note that you can omit the quotation marks (single or double) around the hash key (almost) whenever Perl itself allows it:
print $gettext{Error};
|
The exact rule is: You can omit the surrounding quotes, when the hash
key is a valid C (!) identifier, i.e. when it starts with an
underscore or an ASCII letter and is followed by an arbitrary number
of underscores, ASCII letters or digits. Other Unicode characters
are not allowed, regardless of the use utf8 pragma.
Perl offers a plethora of different string constructs. Those that can
be used either as arguments to functions or inside braces for hash
lookups are generally supported by xgettext.
print gettext "Hello World!"; |
print gettext 'Hello World!'; |
print gettext qq |Hello World!|; print gettext qq <E-mail: <guido\@imperia.net>>; |
The operator qq is fully supported. You can use arbitrary
delimiters, including the four bracketing delimiters (round, angle,
square, curly) that nest.
print gettext q |Hello World!|; print gettext q <E-mail: <guido@imperia.net>>; |
The operator q is fully supported. You can use arbitrary
delimiters, including the four bracketing delimiters (round, angle,
square, curly) that nest.
print gettext qx ;LANGUAGE=C /bin/date; print gettext qx [/usr/bin/ls | grep '^[A-Z]*']; |
The operator qx is fully supported. You can use arbitrary
delimiters, including the four bracketing delimiters (round, angle,
square, curly) that nest.
The example is actually a useless use of gettext. It will
invoke the gettext function on the output of the command
specified with the qx operator. The feature was included
in order to make the interface consistent (the parser will extract
all strings and quote-like expressions).
print gettext <<'EOF'; program not found in $PATH EOF print ngettext <<EOF, <<"EOF"; one file deleted EOF several files deleted EOF |
Here-documents are recognized. If the delimiter is enclosed in single quotes, the string is not interpolated. If it is enclosed in double quotes or has no quotes at all, the string is interpolated.
Delimiters that start with a digit are not supported!
Perl is capable of interpolating variables into strings. This offers some nice features in localized programs but can also lead to problems.
A common error is a construct like the following:
print gettext "This is the program $0!\n"; |
Perl will interpolate at runtime the value of the variable $0
into the argument of the gettext() function. Hence, this
argument is not a string constant but a variable argument ($0
is a global variable that holds the name of the Perl script being
executed). The interpolation is performed by Perl before the string
argument is passed to gettext() and will therefore depend on
the name of the script which can only be determined at runtime.
Consequently, it is almost impossible that a translation can be looked
up at runtime (except if, by accident, the interpolated string is found
in the message catalog).
The xgettext program will therefore terminate parsing with a fatal
error if it encounters a variable inside of an extracted string. In
general, this will happen for all kinds of string interpolations that
cannot be safely performed at compile time. If you absolutely know
what you are doing, you can always circumvent this behavior:
my $know_what_i_am_doing = "This is program $0!\n"; print gettext $know_what_i_am_doing; |
Since the parser only recognizes strings and quote-like expressions, but not variables or other terms, the above construct will be accepted. You will have to find another way, however, to let your original string make it into your message catalog.
If invoked with the option --extract-all, resp. -a,
variable interpolation will be accepted. Rationale: You will
generally use this option in order to prepare your sources for
internationalization.
Please see the manual page ‘man perlop’ for details of strings and quote-like expressions that are subject to interpolation and those that are not. Safe interpolations (that will not lead to a fatal error) are:
\t (tab, HT, TAB), \n
(newline, NL), \r (return, CR), \f (form feed, FF),
\b (backspace, BS), \a (alarm, bell, BEL), and \e
(escape, ESC).
\033
use utf8 pragma.
\x1b
\x{263a}
use utf8 pragma.
\c[ (CTRL-[)
\N{LATIN CAPITAL LETTER C WITH CEDILLA}
use utf8 pragma.
The following escapes are considered partially safe:
\l lowercase next char
\u uppercase next char
\L lowercase till \E
\U uppercase till \E
\E end case modification
\Q quote non-word characters till \E
These escapes are only considered safe if the string consists of
ASCII characters only. Translation of characters outside the range
defined by ASCII is locale-dependent and can actually only be performed
at runtime; xgettext doesn't do these locale-dependent translations
at extraction time.
Except for the modifier \Q, these translations, albeit valid,
are generally useless and only obfuscate your sources. If a
translation can be safely performed at compile time you can just as
well write what you mean.
Perl is often used to generate sources for other programming languages or arbitrary file formats. Web applications that output HTML code make a prominent example for such usage.
You will often come across situations where you want to intersperse code written in the target (programming) language with translatable messages, like in the following HTML example:
print gettext <<EOF;
<h1>My Homepage</h1>
<script language="JavaScript"><!--
for (i = 0; i < 100; ++i) {
alert ("Thank you so much for visiting my homepage!");
}
//--></script>
EOF
|
The parser will extract the entire here document, and it will appear entirely in the resulting PO file, including the JavaScript snippet embedded in the HTML code. If you exaggerate with constructs like the above, you will run the risk that the translators of your package will look out for a less challenging project. You should consider an alternative expression here:
print <<EOF;
<h1>$gettext{"My Homepage"}</h1>
<script language="JavaScript"><!--
for (i = 0; i < 100; ++i) {
alert ("$gettext{'Thank you so much for visiting my homepage!'}");
}
//--></script>
EOF
|
Only the translatable portions of the code will be extracted here, and the resulting PO file will begrudgingly improve in terms of readability.
You can interpolate hash lookups in all strings or quote-like expressions that are subject to interpolation (see the manual page ‘man perlop’ for details). Double interpolation is invalid, however:
# TRANSLATORS: Replace "the earth" with the name of your planet.
print gettext qq{Welcome to $gettext->{"the earth"}};
|
The qq-quoted string is recognized as an argument to xgettext in
the first place, and checked for invalid variable interpolation. The
dollar sign of hash-dereferencing will therefore terminate the parser
with an “invalid interpolation” error.
It is valid to interpolate hash lookups in regular expressions:
if ($var =~ /$gettext{"the earth"}/) {
print gettext "Match!\n";
}
s/$gettext{"U. S. A."}/$gettext{"U. S. A."} $gettext{"(dial +0)"}/g;
|
In Perl, parentheses around function arguments are mostly optional.
xgettext will always assume that all
recognized keywords (except for hashes and hash references) are names
of properly prototyped functions, and will (hopefully) only require
parentheses where Perl itself requires them. All constructs in the
following example are therefore ok to use:
print gettext ("Hello World!\n");
print gettext "Hello World!\n";
print dgettext ($package => "Hello World!\n");
print dgettext $package, "Hello World!\n";
# The "fat comma" => turns the left-hand side argument into a
# single-quoted string!
print dgettext smellovision => "Hello World!\n";
# The following assignment only works with prototyped functions.
# Otherwise, the functions will act as "greedy" list operators and
# eat up all following arguments.
my $anonymous_hash = {
planet => gettext "earth",
cakes => ngettext "one cake", "several cakes", $n,
still => $works,
};
# The same without fat comma:
my $other_hash = {
'planet', gettext "earth",
'cakes', ngettext "one cake", "several cakes", $n,
'still', $works,
};
# Parentheses are only significant for the first argument.
print dngettext 'package', ("one cake", "several cakes", $n), $discarded;
|
The necessity of long messages can often lead to a cumbersome or
unreadable coding style. Perl has several options that may prevent
you from writing unreadable code, and
xgettext does its best to do likewise. This is where the dot
operator (the string concatenation operator) may come in handy:
print gettext ("This is a very long"
. " message that is still"
. " readable, because"
. " it is split into"
. " multiple lines.\n");
|
Perl is smart enough to concatenate these constant string fragments
into one long string at compile time, and so is
xgettext. You will only find one long message in the resulting
POT file.
Note that the future Perl 6 will probably use the underscore
(‘_’) as the string concatenation operator, and the dot
(‘.’) for dereferencing. This new syntax is not yet supported by
xgettext.
If embedded newline characters are not an issue, or even desired, you may also insert newline characters inside quoted strings wherever you feel like it:
print gettext ("<em>In HTML output
embedded newlines are generally no
problem, since adjacent whitespace
is always rendered into a single
space character.</em>");
|
You may also consider to use here documents:
print gettext <<EOF; <em>In HTML output embedded newlines are generally no problem, since adjacent whitespace is always rendered into a single space character.</em> EOF |
Please do not forget that the line breaks are real, i.e. they translate into newline characters that will consequently show up in the resulting POT file.
The foregoing sections should have proven that
xgettext is quite smart in extracting translatable strings from
Perl sources. Yet, some more or less exotic constructs that could be
expected to work, actually do not work.
One of the more relevant limitations can be found in the implementation of variable interpolation inside quoted strings. Only simple hash lookups can be used there:
print <<EOF;
$gettext{"The dot operator"
. " does not work"
. "here!"}
Likewise, you cannot @{[ gettext ("interpolate function calls") ]}
inside quoted strings or quote-like expressions.
EOF
|
This is valid Perl code and will actually trigger invocations of the
gettext function at runtime. Yet, the Perl parser in
xgettext will fail to recognize the strings. A less obvious
example can be found in the interpolation of regular expressions:
s/<!--START_OF_WEEK-->/gettext ("Sunday")/e;
|
The modifier e will cause the substitution to be interpreted as
an evaluable statement. Consequently, at runtime the function
gettext() is called, but again, the parser fails to extract the
string “Sunday”. Use a temporary variable as a simple workaround if
you really happen to need this feature:
my $sunday = gettext "Sunday"; s/<!--START_OF_WEEK-->/$sunday/; |
Hash slices would also be handy but are not recognized:
my @weekdays = @gettext{'Sunday', 'Monday', 'Tuesday', 'Wednesday',
'Thursday', 'Friday', 'Saturday'};
# Or even:
@weekdays = @gettext{qw (Sunday Monday Tuesday Wednesday Thursday
Friday Saturday) };
|
This is perfectly valid usage of the tied hash %gettext but the
strings are not recognized and therefore will not be extracted.
Another caveat of the current version is its rudimentary support for non-ASCII characters in identifiers. You may encounter serious problems if you use identifiers with characters outside the range of 'A'-'Z', 'a'-'z', '0'-'9' and the underscore '_'.
Maybe some of these missing features will be implemented in future versions, but since you can always make do without them at minimal effort, these todos have very low priority.
A nasty problem are brace format strings that already contain braces as part of the normal text, for example the usage strings typically encountered in programs:
die "usage: $0 {OPTIONS} FILENAME...\n";
|
If you want to internationalize this code with Perl brace format strings, you will run into a problem:
die __x ("usage: {program} {OPTIONS} FILENAME...\n", program => $0);
|
Whereas ‘{program}’ is a placeholder, ‘{OPTIONS}’
is not and should probably be translated. Yet, there is no way to teach
the Perl parser in xgettext to recognize the first one, and leave
the other one alone.
There are two possible work-arounds for this problem. If you are
sure that your program will run under Perl 5.8.0 or newer (these
Perl versions handle positional parameters in printf()) or
if you are sure that the translator will not have to reorder the arguments
in her translation – for example if you have only one brace placeholder
in your string, or if it describes a syntax, like in this one –, you can
mark the string as no-perl-brace-format and use printf():
# xgettext: no-perl-brace-format
die sprintf ("usage: %s {OPTIONS} FILENAME...\n", $0);
|
If you want to use the more portable Perl brace format, you will have to do put placeholders in place of the literal braces:
die __x ("usage: {program} {[}OPTIONS{]} FILENAME...\n",
program => $0, '[' => '{', ']' => '}');
|
Perl brace format strings know no escaping mechanism. No matter how this
escaping mechanism looked like, it would either give the programmer a
hard time, make translating Perl brace format strings heavy-going, or
result in a performance penalty at runtime, when the format directives
get executed. Most of the time you will happily get along with
printf() for this special case.
mod_php4, mod_php4-core, phpdoc
php
php, php3, php4
"abc", 'abc'
_("abc")
gettext, dgettext, dcgettext; starting with PHP 4.2.0
also ngettext, dngettext, dcngettext
textdomain function
bindtextdomain function
Programmer must call setlocale (LC_ALL, "")
—
use
xgettext
printf "%2\$d %1\$d"
On platforms without gettext, the functions are not available.
—
An example is available in the ‘examples’ directory: hello-php.
roxen
pike8.0 or pike7.8
pike
"abc"
—
gettext, dgettext, dcgettext
textdomain function
bindtextdomain function
setlocale function
import Locale.Gettext;
use
—
—
On platforms without gettext, the functions are not available.
—
gcc
gcc
c, h.
"abc"
_("abc")
gettext, dgettext, dcgettext, ngettext,
dngettext, dcngettext
textdomain function
bindtextdomain function
Programmer must call setlocale (LC_ALL, "")
#include "intl.h"
Use
xgettext -k_
—
Uses autoconf macros
yes
libycp, libycp-devel, yast2-core, yast2-core-devel
—
ycp
"abc"
_("abc")
_() with 1 or 3 arguments
textdomain statement
—
—
—
use
xgettext
sformat "%2 %1"
fully portable
—
An example is available in the ‘examples’ directory: hello-ycp.
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