gettext: perl-format
15.3.23 Perl Format Strings
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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.