Introduction to awk

Introduction to awk

what is awk

• The word awk is derived from the names of its inventors!!!
• awk is actually Aho Weinberger and Kernighan ;).
• From the original awk paper published by Bell Labs, awk is

 “ Awk is a programming language designed to make many common information  retrieval  and text manipulation tasks  easy to state and to perform.”

• Simply put, awk is a programming language designed to search for, match patterns, and perform actions on files.

awk versions

• awk – Original Bell Labs awk (Version 7 UNIX, around 1978) + latest POSIX

awk.

• nawk – New awk (released with SVR4 around 1989)
• gawk – GNU implementation of awk standard.
• mawk – Michael’s awk.

……… and the list goes on.

All these are basically same except for some minor differences in features

provided. This presentation will assume the  widely used POSIX  awk (also

called “awk”).

A few basic things about awk

• awk reads from a file or from its standard input, and outputs to its standard output.
• awk recognizes the concepts of « file », « record » and « field ».
• A file consists of records, which by default are the lines of the file. One line becomes one record.
• awk operates on one record at a time.
• A record consists of fields, which by default are separated by any number of spaces or tabs.
• Field number 1 is accessed with $1, field 2 with $2, and so forth. $0 refers to the whole record.

Program Structure in Awk

• An awk program is a sequence of statements of the form:

pattern   { action }

pattern   { action }

…

• pattern in front of an action acts as  a  selector  that determines  whether  the  action is to be executed.
• Patterns can be : regular expressions, arithmetic relational  expressions,  string-valued  expressions,  and arbitrary boolean combinations of these.