The awk utility reads the input files one line at a
time. For each line, awk tries the patterns of each of the rules.
If several patterns match then several actions are run, in the order in
which they appear in the awk program. If no patterns match, then
no actions are run.
After processing all the rules (perhaps none) that match the line,
awk reads the next line (however,
see section The next Statement,
and also see section The nextfile Statement).
This continues until the end of the file is reached.
For example, the awk program:
/12/ { print $0 }
/21/ { print $0 }
contains two rules. The first rule has the string `12' as the pattern and `print $0' as the action. The second rule has the string `21' as the pattern and also has `print $0' as the action. Each rule's action is enclosed in its own pair of braces.
This awk program prints every line that contains the string
`12' or the string `21'. If a line contains both
strings, it is printed twice, once by each rule.
This is what happens if we run this program on our two sample data files, `BBS-list' and `inventory-shipped', as shown here:
$ awk '/12/ { print $0 }
> /21/ { print $0 }' BBS-list inventory-shipped
-| aardvark 555-5553 1200/300 B
-| alpo-net 555-3412 2400/1200/300 A
-| barfly 555-7685 1200/300 A
-| bites 555-1675 2400/1200/300 A
-| core 555-2912 1200/300 C
-| fooey 555-1234 2400/1200/300 B
-| foot 555-6699 1200/300 B
-| macfoo 555-6480 1200/300 A
-| sdace 555-3430 2400/1200/300 A
-| sabafoo 555-2127 1200/300 C
-| sabafoo 555-2127 1200/300 C
-| Jan 21 36 64 620
-| Apr 21 70 74 514
Note how the line in `BBS-list' beginning with `sabafoo' was printed twice, once for each rule.
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