Perl Documentation: the Key to Perl

By Xah Lee. Date:

So, i wanted to know what the option perl -C does. So, here's perldoc perlrun. Excerpt:

-C [*number/list*]
     The -C flag controls some of the Perl Unicode features.

     As of 5.8.1, the -C can be followed either by a number or a list of
     option letters. The letters, their numeric values, and effects are
     as follows; listing the letters is equal to summing the numbers.

         I     1   STDIN is assumed to be in UTF-8
         O     2   STDOUT will be in UTF-8
         E     4   STDERR will be in UTF-8
         S     7   I + O + E
         i     8   UTF-8 is the default PerlIO layer for input streams
         o    16   UTF-8 is the default PerlIO layer for output streams
         D    24   i + o
         A    32   the @ARGV elements are expected to be strings encoded
                   in UTF-8
         L    64   normally the "IOEioA" are unconditional,
                   the L makes them conditional on the locale environment
                   variables (the LC_ALL, LC_TYPE, and LANG, in the order
                   of decreasing precedence) -- if the variables indicate
                   UTF-8, then the selected "IOEioA" are in effect
         a   256   Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
                   debugging mode.

     For example, -COE and -C6 will both turn on UTF-8-ness on both
     STDOUT and STDERR. Repeating letters is just redundant, not
     cumulative nor toggling.

     The "io" options mean that any subsequent open() (or similar I/O
     operations) in the current file scope will have the ":utf8" PerlIO
     layer implicitly applied to them, in other words, UTF-8 is expected
     from any input stream, and UTF-8 is produced to any output stream.
     This is just the default, with explicit layers in open() and with
     binmode() one can manipulate streams as usual.

     -C on its own (not followed by any number or option list), or the
     empty string "" for the "PERL_UNICODE" environment variable, has
     the same effect as -CSDL. In other words, the standard I/O handles
     and the default "open()" layer are UTF-8-fied *but* only if the
     locale environment variables indicate a UTF-8 locale. This
     behaviour follows the *implicit* (and problematic) UTF-8 behaviour
     of Perl 5.8.0.

     You can use -C0 (or "0" for "PERL_UNICODE") to explicitly disable
     all the above Unicode features.

     The read-only magic variable "${^UNICODE}" reflects the numeric
     value of this setting. This variable is set during Perl startup and
     is thereafter read-only. If you want runtime effects, use the
     three-arg open() (see "open" in perlfunc), the two-arg binmode()
     (see "binmode" in perlfunc), and the "open" pragma (see open).

     (In Perls earlier than 5.8.1 the -C switch was a Win32-only switch
     that enabled the use of Unicode-aware "wide system call" Win32
     APIs. This feature was practically unused, however, and the command
     line switch was therefore "recycled".)

     Note: Since perl 5.10.1, if the -C option is used on the "#!" line,
     it must be specified on the command line as well, since the
     standard streams are already set up at this point in the execution
     of the perl interpreter. You can also use binmode() to set the
     encoding of an I/O stream.

reading that is like a adventure. It's like this:

The -C is a key to unlock many secrets. Just get it, and you'll be all good to go, except in cases you may need the inner key. You'll find a hinge in the key, open it, then there's a subkey. On the subkey, there's a number. Take that number to the lock, it will open with keyX. When you use keyX, it must be matched with the previous inner key with 8th bit. keyX doesn't have a ID, but you can make one by finding the number at the place you found the key C. Key C is actually optional, but when inner key and keyX's number matches, it changes the nature of the lock. This is when you need to turn on keyMode …

If you have a question, put $5 at patreon and message me.