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Expressions are the basic building block of awk actions. An
expression evaluates to a value, which you can print, test, store in a
variable or pass to a function. But beyond that, an expression can assign a new value to a variable
or a field, with an assignment operator.
An expression can serve as a statement on its own. Most other kinds of
statements contain one or more expressions which specify data to be
operated on. As in other languages, expressions in awk include
variables, array references, constants, and function calls, as well as
combinations of these with various operators.
- Constants: String, numeric, and regexp constants.
- Variables: Variables give names to values for later use.
- Arithmetic Ops: Arithmetic operations (`+', `-', etc.)
- Concatenation: Concatenating strings.
- Comparison Ops: Comparison of numbers and strings
with `<', etc.
- Boolean Ops: Combining comparison expressions
using boolean operators
`||' ("or"), `&&' ("and") and `!' ("not").
- Assignment Ops: Changing the value of a variable or a field.
- Increment Ops: Incrementing the numeric value of a variable.
- Conversion: The conversion of strings to numbers
and vice versa.
- Values: The whole truth about numbers and strings.
- Conditional Exp: Conditional expressions select
between two subexpressions under control
of a third subexpression.
- Function Calls: A function call is an expression.
- Precedence: How various operators nest.
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