( Perl Pitfalls

Info Catalog ( Long Lines ( Perl Bugs, Pitfalls, And Things That Do Not Work
 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.
    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";
    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.
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