随机过程

1. Selection by Comparison

awk '$3 > 0 {printf("%s %.2f %.2f\n", $1, $2, $3)}' data

The comparison $3 > 0 is to decide which field is to be selected.


2. Selection by Computation

awk '$2*$3 > 50 {printf("$%.2f for %s\n", $2*$3, $1)}' data

The computation $2*$3 > 0 is to decide which field is to be selected.

3. Selection by Text Content

        Besides numeric tests, you can select input lines that contain specific words or phrases. This program prints all lines in which the first field is Susie:

$1 == "Susie"

as the following:

awk '$1 == "Susie" {printf("%s %.2d %.2d\n", $1, $2, $3)}' data

The operator == tests for equality. You can also look for text containing any of a set of letters, words, and phrases by using patterns called regular expressions.  This pattern select all lines that contain Susie anywhere:

/Susie/

and the program is as the following

awk '/Susie/ {printf("%s %.2d %.2d\n", $1, $2, $3)}' data

4. Combination of Patterns

        Patterns can be combined with parentheses and the logical operators &&, ||, and !, which stand for AND, OR, and NOT. The expression

$2 >= 4 || $3 >= 20

select those lines where $2 is at least 4 or $3 is at least 20, the program can be given as:

awk '$2 >= 4 || $3 >= 20 {printf("%s %.2f %.2f\n", $1, $2, $3)}' data