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Variables
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   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" and "increment operators".  *Note Assignment
Expressions: Assignment Ops.

   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 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'.  Each built-in variable's name is made entirely of upper case
letters.

   Variables in `awk' can be assigned either numeric or string values.
By default, variables are initialized to the null string, which is
effectively zero if converted to a number.  There is no need to
"initialize" each variable explicitly in `awk', the way you would in C
or most other traditional languages.

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Assignment Options
Setting variables on the command line and a summary of command line syntax. This is an advanced method of input.