6.1. The Building Blocks of Logic

Like any complete programming language, AWK provides a rich set of operators for performing arithmetic, string manipulation, comparisons, and logical evaluations. These operators are the tools used to construct expressions, which form the core logic of any non-trivial AWK program.

6.2. Operator Categories

Arithmetic Operators

These operators perform standard mathematical calculations: + (addition), – (subtraction), * (multiplication), / (division), and % (modulus).

[jerry]$ awk ‘BEGIN { print “10 % 3 =”, 10 % 3 }’

# Output:

# 10 % 3 = 1

Increment and Decrement Operators

AWK supports pre- and post-increment (++i, i++) and pre- and post-decrement (–i, i–) operators to modify numeric values by one.

Assignment Operators

These operators assign values to variables. They include simple assignment (=) and compound assignments such as +=, -=, *=, /=, and %=, which perform an operation and an assignment in a single step.

[jerry]$ awk ‘BEGIN { x = 5; x += 3; print “x =”, x }’

# Output:

# x = 8

Relational Operators

Used for comparing values, these operators form the basis of conditional logic. They include < (less than), > (greater than), <= (less than or equal to), >= (greater than or equal to), == (is equal to), and != (is not equal to).

[jerry]$ awk ‘$4 > 85 {print $2, “scored above 85”}’ marks.txt

# Output:

# Rahul scored above 85

# Shyam scored above 85

# Hari scored above 85

Logical Operators

These operators combine conditional expressions: && (logical AND), || (logical OR), and ! (logical NOT).

[jerry]$ awk ‘$4 > 85 && $3 == “Maths” {print $2, “is a top Maths student.”}’ marks.txt

# Output:

# Rahul is a top Maths student.

Ternary Operator

This operator provides a concise way to write a conditional expression: condition ? expr1 : expr2. If condition is true, the expression evaluates to expr1; otherwise, it evaluates to expr2.

[jerry]$ awk ‘{print $2, $4, ($4 > 85 ? “Pass” : “Fail”)}’ marks.txt

# Output:

# Amit 80 Fail

# Rahul 90 Pass

# Shyam 87 Pass

# Kedar 85 Fail

# Hari 89 Pass

Unary Operators

The unary + and – operators are used to specify the sign of a numeric literal.

Exponential Operators

The ^ and ** operators are used for exponentiation (raising a number to a power).

[jerry]$ awk ‘BEGIN { print “3^2 =”, 3^2 }’

# Output:

# 3^2 = 9

String Concatenation Operator

In AWK, a space between two string expressions serves as the concatenation operator, joining them into a single string.

[jerry]$ awk ‘{print “Student: ” $2 “, Subject: ” $3}’ marks.txt

# Output:

# Student: Amit, Subject: Physics

# Student: Rahul, Subject: Maths

# …

Array Membership Operator

The in keyword is an operator used to check if a specific index exists within an array.

[jerry]$ awk ‘BEGIN { grades[“Amit”]=80; if (“Amit” in grades) print “Amit has a grade.” }’

# Output:

# Amit has a grade.

Regular Expression Operators

The matching (~) and non-matching (!~) operators are used to test whether a field or variable matches a regular expression.

[jerry]$ awk ‘$2 ~ /^A/ {print $0}’ marks.txt

# Output:

# 1) Amit Physics 80

The regular expression operators are fundamental to AWK’s text processing capabilities, leading us to a more detailed examination of regular expressions themselves.