By default, running out of memory is an untrappable, fatal error. However, if suitably built, Perl can use the contents of
$^M as an emergency memory pool after
die()ing. Suppose that your Perl were compiled with
-DPERL_EMERGENCY_SBRK and used Perl's malloc. Then
$^M = 'a' x (1 << 16);
would allocate a 64K buffer for use in an emergency. See the INSTALL file in the Perl distribution for information on how to add custom C compilation flags when compiling perl. To discourage casual use of this advanced feature, there is no English long name for this variable.
This variable was added in Perl 5.004.