The awk utility reads the input files one line at a
time. For each line, awk tries the patterns of each rule.
If several patterns match, then several actions execute in the order in
which they appear in the awk program. If no patterns match, then
no actions 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 The 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, mail-list and inventory-shipped:
$ awk '/12/ { print $0 }
> /21/ { print $0 }' mail-list inventory-shipped
-| Anthony 555-3412 anthony.asserturo@hotmail.com A
-| Camilla 555-2912 camilla.infusarum@skynet.be R
-| Fabius 555-1234 fabius.undevicesimus@ucb.edu F
-| Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R
-| Jean-Paul 555-2127 jeanpaul.campanorum@nyu.edu R
-| Jan 21 36 64 620
-| Apr 21 70 74 514
Note how the line beginning with ‘Jean-Paul’ in mail-list was printed twice, once for each rule.