$b Special package variables when using sort()

$OUTPUT_FIELD_SEPARATOR

IO::Handle->output_record_separator( EXPR )

%^H The %^H hash provides the same scoping semantic as

$^W The current value of the warning switch, initially true if -w was used, false otherwise, but directly modifiable.

$0 Contains the name of the program being executed. On some (but not all) operating systems assigning to

$WARNING

$EFFECTIVE_USER_ID

$$ The process number of the Perl running this script. Though you can set this variable, doing so is generally discouraged, although

${^PREMATCH} This is similar to $` ($PREMATCH) except that it does not incur the performance