Using awk

Relational operators

An awk pattern can be any expression involving comparisons between strings of characters or numbers. To make comparisons, awk includes six relational operators and two regular expression matching operators, ~ (tilde) and !~, (discussed in ``Regular expressions''). ``awk comparison operators'' shows the relational operators and their meanings.

awk comparison operators

Operator Meaning

< less than

<= less than or equal to

== equal to

!= not equal to

>= greater than or equal to

> greater than

In a comparison, if both operands are numeric, a numeric comparison is made; otherwise, the operands are compared as strings. (Every value might be either a number or a string; usually awk can determine what is intended. See ``Number or string?'' for more information about this.) Thus, the following pattern selects lines where the third field exceeds 100:

Operator	Meaning
<	less than
<=	less than or equal to
==	equal to
!=	not equal to
>=	greater than or equal to
>	greater than

   $3>100

This program selects lines that begin with the letters ``S'' through ``Z'' (that is, lines with an ASCII value greater than or equal to ``S''):

   $1 >= "S"

The output looks like this:

   USA         3615      219        North America
   Sudan        968       19        Africa
   USA         3615      219        North America
   Sudan        968       19        Africa

In the absence of any other information, awk treats fields as strings. Thus, the following program compares the first and fourth fields as strings of characters:

   $1 == $4

Using the file countries as input, this program prints the single line for which this test succeeds:

   Australia   2968   14   Australia

If both fields appear to be numbers, awk performs the comparisons numerically.