awk(1)

awk [opt] program [input]
    -F <sepstr>        field separator string (can be regex)
    program            awk program
    input              file or stdin if not file given

Input processing

Input is processed in two stages:

1. Splitting input into a sequence of records. By default split at newline character, but can be changed via the builtin RS variable.
2. Splitting a record into fields. By default strings without whitespace, but can be changed via the builtin variable FS or command line option -F.

Field are accessed as follows:

• $0 whole record
• $1 field one
• $2 field two
• ...

Program

An awk program is composed of pairs of the form:

pattern { action }

The program is run against each record in the input stream. If a pattern matches a record the corresponding action is executed and can access the fields.

INPUT
  |
  v
record ----> ∀ pattern matched
  |                   |
  v                   v
fields ----> run associated action