---

   gawk    ( 1 )

---

AWK PROGRAM EXECUTION

An AWK program consists of a sequence of optional directives, pattern-action statements, and optional function definitions.

@include "filename" @load "filename" @namespace "name" pattern { action statements } function name(parameter list) { statements }

Gawk first reads the program source from the program-file(s) if specified, from arguments to --source, or from the first non- option argument on the command line. The -f and --source options may be used multiple times on the command line. Gawk reads the program text as if all the program-files and command line source texts had been concatenated together. This is useful for building libraries of AWK functions, without having to include them in each new AWK program that uses them. It also provides the ability to mix library functions with command line programs.

In addition, lines beginning with @include may be used to include other source files into your program, making library use even easier. This is equivalent to using the --include option.

Lines beginning with @load may be used to load extension functions into your program. This is equivalent to using the --load option.

The environment variable AWKPATH specifies a search path to use when finding source files named with the -f and --include options. If this variable does not exist, the default path is ".:/usr/local/share/awk". (The actual directory may vary, depending upon how gawk was built and installed.) If a file name given to the -f option contains a '/' character, no path search is performed.

The environment variable AWKLIBPATH specifies a search path to use when finding source files named with the --load option. If this variable does not exist, the default path is "/usr/local/lib/gawk". (The actual directory may vary, depending upon how gawk was built and installed.)

Gawk executes AWK programs in the following order. First, all variable assignments specified via the -v option are performed. Next, gawk compiles the program into an internal form. Then, gawk executes the code in the BEGIN rule(s) (if any), and then proceeds to read each file named in the ARGV array (up to ARGV[ARGC-1]). If there are no files named on the command line, gawk reads the standard input.

If a filename on the command line has the form var=val it is treated as a variable assignment. The variable var will be assigned the value val. (This happens after any BEGIN rule(s) have been run.) Command line variable assignment is most useful for dynamically assigning values to the variables AWK uses to control how input is broken into fields and records. It is also useful for controlling state if multiple passes are needed over a single data file.

If the value of a particular element of ARGV is empty (""), gawk skips over it.

For each input file, if a BEGINFILE rule exists, gawk executes the associated code before processing the contents of the file. Similarly, gawk executes the code associated with ENDFILE after processing the file.

For each record in the input, gawk tests to see if it matches any pattern in the AWK program. For each pattern that the record matches, gawk executes the associated action. The patterns are tested in the order they occur in the program.

Finally, after all the input is exhausted, gawk executes the code in the END rule(s) (if any).

Command Line Directories According to POSIX, files named on the awk command line must be text files. The behavior is ``undefined'' if they are not. Most versions of awk treat a directory on the command line as a fatal error.

Starting with version 4.0 of gawk, a directory on the command line produces a warning, but is otherwise skipped. If either of the --posix or --traditional options is given, then gawk reverts to treating directories on the command line as a fatal error.