Perl 5 version 30.0 documentation
locale - Perl pragma to use or avoid POSIX locales for built-in operations
DO NOT USE this pragma in scripts that have multiple
threads active. The locale is not local to a single thread.
Another thread may change the locale at any time, which could cause at a
minimum that a given thread is operating in a locale it isn't expecting
to be in. On some platforms, segfaults can also occur. The locale
change need not be explicit; some operations cause perl to change the
locale itself. You are vulnerable simply by having done a
This pragma tells the compiler to enable (or disable) the use of POSIX locales for built-in operations (for example, LC_CTYPE for regular expressions, LC_COLLATE for string comparison, and LC_NUMERIC for number formatting). Each "use locale" or "no locale" affects statements to the end of the enclosing BLOCK.
See perllocale for more detailed information on how Perl supports locales.
On systems that don't have locales, this pragma will cause your operations to behave as if in the "C" locale; attempts to change the locale will fail.