Node:Two Rules, Next:More Complex, Previous:Very Simple, Up:Getting Started
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 that match the line (and perhaps there are none),
awk reads the next line. (However,
see The next Statement,
and also see Using gawk's nextfile Statement).
This continues until the program reaches the end of the file.
For example, the following awk program contains two rules:
/12/ { print $0 }
/21/ { print $0 }
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 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:
$ 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 beginning with sabafoo
in BBS-list was printed twice, once for each rule.