6.1.3.1 Using Variables in a Program

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. 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. In addition, the sub() and gsub() functions can change a variable’s value, and the match(), patsplit() and split() functions can change the contents of their array parameters. See section String-Manipulation 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). See section Built-in Variables, for a list of the built-in variables. 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 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.