$^O The name of the operating system under which this copy of Perl was built, as determined during the configuration process. For examples

$^H WARNING: This variable is strictly for internal use only. Its availability, behavior, and contents are subject to change without notice

$OUTPUT_FIELD_SEPARATOR

$^C The current value of the flag associated with the -c switch. Mainly of use with -MO=... to allow code to alter its behavior

$INPLACE_EDIT

%ERRNO

$WARNING

%+ Similar to @+ , the %+ hash allows

${^OPEN} An internal variable used by PerlIO. A string in two parts, separated by a \0 byte

$LAST_SUBMATCH_RESULT