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     Expressions

     The autoincrement operator has a little extra built-in magic
     to it.  If you increment a variable that is numeric, or that
     has ever been used in a numeric context, you  get  a  normal
     increment.   If, however, the variable has only been used in
     string contexts since it was set, and has a  value  that  is
     not  null  and  matches the pattern /^[a-zA-Z]*[0-9]*$/, the
     increment is done as a  string,  preserving  each  character
     within its range, with carry:

          print ++($foo = '99');   # prints '100'
          print ++($foo = 'a0');   # prints 'a1'
          print ++($foo = 'Az');   # prints 'Ba'
          print ++($foo = 'zz');   # prints 'aaa'

     The autodecrement is not magical.

     The range operator (in an array context) makes  use  of  the
     magical  autoincrement  algorithm if the minimum and maximum
     are strings.  You can say

          @alphabet = ('A' .. 'Z');

     to get all the letters of the alphabet, or

          $hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];

     to get a hexadecimal digit, or

          @z2 = ('01' .. '31');  print @z2[$mday];

     to get dates with leading zeros.  (If the final value speci-
     fied is not in the sequence that the magical increment would
     produce, the sequence goes until the  next  value  would  be
     longer than the final value specified.)

     The || and && operators differ from C's in that, rather than
     returning  0  or  1,  they  return the last value evaluated.
     Thus, a portable way to find out the  home  directory  might
     be:

          $home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
              (getpwuid($<))[7] || die "You're homeless!\n";


     Along with the literals and variables mentioned earlier, the
     operations in the following section can serve as terms in an
     expression.  Some of these operations  take  a  LIST  as  an
     argument.   Such  a  list  can consist of any combination of
     scalar arguments or array values; the array values  will  be
     included  in  the  list  as  if each individual element were
     interpolated at that point in the  list,  forming  a  longer
     single-dimensional array value.  Elements of the LIST should
     be separated by commas.  If an operation is listed both with
     and  without  parentheses around its arguments, it means you
     can either use it as a unary operator or as a function call.
     To  use  it  as  a function call, the next token on the same
     line must be a left parenthesis.  (There may be  intervening
     white  space.)  Such a function then has highest precedence,
     as you would expect from a function.   If  any  token  other
     than  a  left parenthesis follows, then it is a unary opera-
     tor, with a precedence depending only on  whether  it  is  a
     LIST  operator  or  not.   LIST  operators  have lowest pre-
     cedence.   All  other  unary  operators  have  a  precedence
     greater  than  relational operators but less than arithmetic
     operators.  See the section on Precedence.