AWK is a computer pattern/action language that can be used for data analysis, manipulation and simple reporting. It is one of the early tools to appear in Version 3 UNIX and gained popularity as a way to add computational features to a UNIX pipeline. The name AWK is derived from the surnames of its authors -- Alfred V. Aho, Peter J. Weinberger, and Brian W. Kernighan.
A version of awk is a standard feature of nearly every modern unix-like operating system available today. The most common versions are listed at [1].
Awk is an example of a programming language that extensively uses the string datatype, associative arrays (that is, arrays indexed by key strings), and regular expressions.
A free GNU version of awk is named gawk. Documentation and downloads are available at [1].
comp.lang.awk is a USENET newsgroup dedicated to awk.
The power, terseness, and limitations of awk programs and sed scripts inspired Larry Wall to write Perl.
Table of contents |
2 Awk commands 3 External links |
Structure of awk programs
Generally speaking, two pieces of data are given to awk: a command file and an input file. A command file (which can be an actual file, or can be included in the command line invocation of awk) contains a series of commands which tell awk how to process the input file. The input file is typically text that is formatted in some way; it can be an actual file, or it can be read by awk from the standard input. A typical awk program consists of a series of lines, each of the form
/pattern/ { action }where pattern is a regular expression and action is a command. Awk looks through the input file; when it finds a line that matches pattern, it executes the command(s) specified in action. Alternate line forms include:
; BEGIN { action }
Awk commands
Awk commands are the statement that is substituted for action in the examples above. Awk commands can include function calls, variable assignments, calculations, or any combination thereof. Awk contains built-in support for many functions; many more are provided by the various flavors of awk. Also, some flavors support the inclusion of dynamically linked libraries, which can also provide more functions.
For brevity, the enclosing curly braces ( { } ) will be omitted from these examples.
The print command
The print command is used to display text to the output device (usually a monitor, though often a file or
output stream as well). The simplest form of this command is
; print $1
The print command can also display the results of calculations and/or function calls:
print 3+2 print foobar(3) print foobar(variable) print sin(3-2)
User-defined functions
In a format similar to C, function declarations consist of the function name and arguments to the function. Here is an example function:
function add_three (number) { temp = number + 3 return temp }This statement can be invoked as follows:
print add_three(36) # prints 39Functions can have variables that are in the local scope. The names of these are added to the end of the argument list, though values for these should be omitted when calling the function. It is convention to add some whitespace in the argument list before the local variables, in order to indicate where the parameters end and the local variables begin.