Variables let you give names to values and refer to them later. You have
already seen variables in many of the examples. The name of a variable
must be a sequence of letters, digits and underscores, but it may not begin
with a digit. Case is significant in variable names; a and A
are distinct variables.
A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with assignment operators, increment operators and decrement operators. See section Assignment Expressions.
A few variables have special built-in meanings, such as FS, the
field separator, and NF, the number of fields in the current
input record. See section Built-in Variables, for a list of them. These
built-in variables can be used and assigned just like all other
variables, but their values are also used or changed automatically by
awk. All built-in variables names are entirely upper-case.
Variables in awk can be assigned either numeric or string
values. By default, variables are initialized to the empty string, which
is zero if converted to a number. There is no need to
"initialize" each variable explicitly in awk,
the way you would in C and in most other traditional languages.
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