Copyright Sams Teach Yourself Shell Programming in 24 Hours

Pineapple $1.29 35 REORDER
Apple $0.99 78
Compound Expressions
Often you need to combine two or more expressions to check for a particular condition. When
you combine two or more expressions, the result is called a compound expression .
Compound expressions are constructed by using either the && (and) or the || (or) compound operators.
The syntax is
(expr1) && (expr2)
(expr2) || (expr2)
Here expr1 and expr2 are expressions constructed using the conditional operators given in Table 17.1.
The parentheses surrounding expr1 and expr2 are required.
When the && operator is used, both expr1 and expr2 must be true for the compound expression to be
true. When the || operator is used, the compound expression is true if either expr1 or expr2 is true.
As an example of using a compound expression, you can use the compound operators to obtain a list of all
the fruit that cost more than a dollar and of which there are less than 75:
awk '
($2 ~ /^\$[1-9][0-9]*\.[0-9][0-9]$/) && ($3 < 75) {
printf "%s\t%s\t%s\n",$0,"*","REORDER" ;
}
' fruit_prices.txt ;
The output looks like the following
Kiwi $1.50 22 * REORDER
Pineapple $1.29 35 * REORDER
The Compound Expression Operators
You might hear the && operator called the and-and operator because it consists of two ampersands ( and
characters). Similarly, the || operator might be referred to as the or-or operator.
The next Command
Consider the following script:
#!/bin/sh
awk '
$3 75 { print $0 ; }
' fruit_prices.txt