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command line, and some may not; you could even get a "-" without its
letter, if you're not careful.  You probably want to make sure that all
your switches fall either before or after that 32 character boundary.
Most switches don't actually care if they're processed redundantly, but
getting a - instead of a complete switch could cause Perl to try to
execute standard input instead of your script.  And a partial B<-I> switch
could also cause odd results.

Parsing of the #! switches starts wherever "perl" is mentioned in the line.
The sequences "-*" and "- " are specifically ignored so that you could,
if you were so inclined, say

    #!/bin/sh -- # -*- perl -*- -p
    eval 'exec perl $0 -S ${1+"$@"}'
	if 0;

to let Perl see the B<-p> switch.

If the #! line does not contain the word "perl", the program named after
the #! is executed instead of the Perl interpreter.  This is slightly
bizarre, but it helps people on machines that don't do #!, because they
can tell a program that their SHELL is /usr/bin/perl, and Perl will then
dispatch the program to the correct interpreter for them.

After locating your script, Perl compiles the entire script to an
internal form.  If there are any compilation errors, execution of the
script is not attempted.  (This is unlike the typical shell script,
which might run partway through before finding a syntax error.)

If the script is syntactically correct, it is executed.  If the script
runs off the end without hitting an exit() or die() operator, an implicit
C<exit(0)> is provided to indicate successful completion.

=head2 Switches

A single-character switch may be combined with the following switch, if
any.

    #!/usr/bin/perl -spi.bak	# same as -s -p -i.bak

Switches include:

=over 5

=item B<-0>I<digits>

specifies the record separator (C<$/>) as an octal number.  If there are
no digits, the null character is the separator.  Other switches may
precede or follow the digits.  For example, if you have a version of
B<find> which can print filenames terminated by the null character, you
can say this:

    find . -name '*.bak' -print0 | perl -n0e unlink

The special value 00 will cause Perl to slurp files in paragraph mode.
The value 0777 will cause Perl to slurp files whole since there is no
legal character with that value.

=item B<-a>

turns on autosplit mode when used with a B<-n> or B<-p>.  An implicit
split command to the @F array is done as the first thing inside the
implicit while loop produced by the B<-n> or B<-p>.

    perl -ane 'print pop(@F), "\n";'

is equivalent to

    while (<>) {
	@F = split(' ');
	print pop(@F), "\n";
    }

An alternate delimiter may be specified using B<-F>.

=item B<-c>

causes Perl to check the syntax of the script and then exit without
executing it.  Actually, it will execute C<BEGIN> and C<use> blocks,
since these are considered part of the compilation.

=item B<-d>

runs the script under the Perl debugger.  See L<perldebug>.

=item B<-D>I<number>

=item B<-D>I<list>

sets debugging flags.  To watch how it executes your script, use
B<-D14>.  (This only works if debugging is compiled into your
Perl.)  Another nice value is B<-D1024>, which lists your compiled
syntax tree.  And B<-D512> displays compiled regular expressions. As an
alternative specify a list of letters instead of numbers (e.g. B<-D14> is
equivalent to B<-Dtls>):

        1  p  Tokenizing and Parsing
        2  s  Stack Snapshots
        4  l  Label Stack Processing
        8  t  Trace Execution
       16  o  Operator Node Construction
       32  c  String/Numeric Conversions
       64  P  Print Preprocessor Command for -P
      128  m  Memory Allocation
      256  f  Format Processing
      512  r  Regular Expression Parsing
     1024  x  Syntax Tree Dump
     2048  u  Tainting Checks
     4096  L  Memory Leaks (not supported anymore)
     8192  H  Hash Dump -- usurps values()
    16384  X  Scratchpad Allocation
    32768  D  Cleaning Up

=item B<-e> I<commandline>

may be used to enter one line of script.  
If B<-e> is given, Perl
will not look for a script filename in the argument list.  
Multiple B<-e> commands may
be given to build up a multi-line script.  
Make sure to use semicolons where you would in a normal program.