File: gawk.info,  Node: Using Variables,  Next: Assignment Options,  Up: Variables

6.1.3.1 Using Variables in a Program
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Variables let you give names to values and refer to them later.
Variables have already been used in many of the examples.  The name of a
variable must be a sequence of letters, digits, or underscores, and it
may not begin with a digit.  Here, a "letter" is any one of the 52
upper- and lowercase English letters.  Other characters that may be
defined as letters in non-English locales are not valid in variable
names.  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"
(*note Assignment Ops::).  In addition, the 'sub()' and 'gsub()'
functions can change a variable's value, and the 'match()', 'split()',
and 'patsplit()' functions can change the contents of their array
parameters (*note String Functions::).

   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).  *Note Built-in Variables:: for a list of the predefined
variables.  These predefined variables can be used and assigned just
like all other variables, but their values are also used or changed
automatically by 'awk'.  All predefined variables' names are entirely
uppercase.

   Variables in 'awk' can be assigned either numeric or string values.
The kind of value a variable holds can change over the life of a
program.  By default, variables are initialized to the empty string,
which is zero if converted to a number.  There is no need to explicitly
initialize a variable in 'awk', which is what you would do in C and in
most other traditional languages.