${^UNICODE} Reflects certain Unicode settings of Perl. See perlrun documentation for the -C switch for more information about the possible values. This variable is set during Perl startup and is thereafter read-only. This variable was added in Perl v5.8.2.

${^TAINT} Reflects if taint mode is on or off. 1 for on (the program was run with -T), 0 for off, -1 when only taint warnings are enabled (i.e. with -t or -TU). This variable is read-only. This variable was added in Perl v5.8.0.

${^RE_TRIE_MAXBUF} Controls how certain regex optimisations are applied and how much memory they utilize. This value by default is 65536 which corresponds to a 512kB temporary cache. Set this to a higher value to trade memory for speed when matching large alternations. Set it to a lower value if you want the optimisations to be as conservative of memory as possible but still occur, and set it to a negative value to prevent the optimisation and conserve the most memory. Under normal situations

${^RE_DEBUG_FLAGS} The current value of the regex debugging flags. Set to 0 for no debug output even when the re 'debug' module is loaded. See re for details. This variable was added in Perl v5.10.0.

${^PREMATCH} This is similar to $` ($PREMATCH) except that it does not incur the performance penalty associated with that variable. See Performance issues above. In Perl v5.18 and earlier, it is only guaranteed to return a defined value when the pattern was compiled or executed with the /p modifier. In Perl v5.20, the /p modifier does nothing, so ${^PREMATCH} does the same thing as $PREMATCH . This variable was added in Perl v5.10.0. This variable is read-only and dynamically-scoped.

${^POSTMATCH} This is similar to $' ($POSTMATCH ) except that it does not incur the performance penalty associated with that variable. See Performance issues above. In Perl v5.18 and earlier, it is only guaranteed to return a defined value when the pattern was compiled or executed with the /p modifier. In Perl v5.20, the /p modifier does nothing, so ${^POSTMATCH} does the same thing as $POSTMATCH . This variable was added in Perl v5.10.0. This variable is read-only and dynamically-scoped.

${^OPEN} An internal variable used by PerlIO. A string in two parts, separated by a \0 byte, the first part describes the input layers, the second part describes the output layers. This variable was added in Perl v5.8.0.

${^MATCH} This is similar to $& ($MATCH ) except that it does not incur the performance penalty associated with that variable. See Performance issues above. In Perl v5.18 and earlier, it is only guaranteed to return a defined value when the pattern was compiled or executed with the /p modifier. In Perl v5.20, the /p modifier does nothing, so ${^MATCH} does the same thing as $MATCH . This variable was added in Perl v5.10.0. This variable is read-only and dynamically-scoped.

${^LAST_FH} This read-only variable contains a reference to the last-read filehandle. This is set by <HANDLE> , readline, tell, eof and seek. This is the same handle that $. and tell and eof without arguments use. It is also the handle used when Perl appends ", <STDIN> line 1" to an error or warning message. This variable was added in Perl v5.18.0. Variables related to formats The special variables for formats are a subset of those for filehandles. See perlform for more information

${^GLOBAL_PHASE} The current phase of the perl interpreter. Possible values are: