6.3. How awk Works Before getting into all the details of awk , let's look at how it does its job, step by step. We'll look at a simple three-line file called names : Tom Savage 100 Molly Lee 200 John Doe 300
The awk command follows : % nawk '{print , }' names
- 1. Awk takes a line of input (from a file or pipe) and puts the line into an internal variable called $0 . Each line is also called a record and is terminated by a newline, by default.
 - 2. Next , the line is broken into fields (words) separated by whitespace. Each field is stored in a numbered variable, starting with $1 . There can be as many as 100 fields.
 - 3. How does awk know that whitespace separates the fields? There is another internal variable, called FS , that designates the field separator. Initially, FS is assigned whitespace ”tabs and spaces. If the fields are separated by another character, such as a colon or dash, you can change the value of FS to designate the new field separator. (See "Field Separators" on page 169.)
- 4. When awk prints the fields, it uses the print function as follows:
{print ,}
And the output shows each field separated by a space, as
Tom 100 Molly 200 John 300
Awk provides the space in the output between Tom and 100 for you because there is a comma placed between $1 and $3 . The comma is special. It is mapped to another internal variable, called the output field separator (OFS). The OFS is assigned a space as its default. The comma generates whatever character has been assigned to the OFS variable.
- 5. After awk displays its output, it gets the next line in the file and stores that in $0 , overwriting what was there. It then breaks that line into fields, and processes it. This continues until all the lines in the file have been processed .
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