Fields
------

   As each input line is read, `gawk' splits the line into FIELDS,
using the value of the `FS' variable as the field separator.  If `FS'
is a single character, fields are separated by that character.
Otherwise, `FS' is expected to be a full regular expression.  In the
special case that `FS' is a single blank, fields are separated by runs
of blanks and/or tabs.  Note that the value of `IGNORECASE' (
see Case-sensitivity in Matching: Case-sensitivity.) also affects how
fields are split when `FS' is a regular expression.

   Each field in the input line may be referenced by its position, `$1',
`$2', and so on.  `$0' is the whole line.  The value of a field may be
assigned to as well.  Field numbers need not be constants:

     n = 5
     print $n

prints the fifth field in the input line.  The variable `NF' is set to
the total number of fields in the input line.

   References to nonexistent fields (i.e., fields after `$NF') return
the null-string.  However, assigning to a nonexistent field (e.g.,
`$(NF+2) = 5') increases the value of `NF', creates any intervening
fields with the null string as their value, and causes the value of
`$0' to be recomputed, with the fields being separated by the value of
`OFS'.

   See Reading Input Files: Reading Files, for a full description of
the way `awk' defines and uses fields.