Gawk/Invoking-Summary

2.11 Summary

gawk parses arguments on the command line, left to right, to determine if they should be treated as options or as non-option arguments.
gawk recognizes several options which control its operation, as described in Command-Line Options. All options begin with ‘-’.
Any argument that is not recognized as an option is treated as a non-option argument, even if it begins with ‘-’.
- - However, when an option itself requires an argument, and the option is separated from that argument on the command line by at least one space, the space is ignored, and the argument is considered to be related to the option. Thus, in the invocation, ‘gawk -F x’, the ‘x’ is treated as belonging to the -F option, not as a separate non-option argument.
Once gawk finds a non-option argument, it stops looking for options. Therefore, all following arguments are also non-option arguments, even if they resemble recognized options.
If no -e or -f options are present, gawk expects the program text to be in the first non-option argument.
All non-option arguments, except program text provided in the first non-option argument, are placed in ARGV as explained in Using ARGC and ARGV, and are processed as described in Other Command-Line Arguments. Adjusting ARGC and ARGV affects how awk processes input.
The three standard options for all versions of awk are -f, -F, and -v. gawk supplies these and many others, as well as corresponding GNU-style long options.
Nonoption command-line arguments are usually treated as file names, unless they have the form ‘var=value’, in which case they are taken as variable assignments to be performed at that point in processing the input.
You can use a single minus sign (‘-’) to refer to standard input on the command line. gawk also lets you use the special file name /dev/stdin.
gawk pays attention to a number of environment variables. AWKPATH, AWKLIBPATH, and POSIXLY_CORRECT are the most important ones.
gawk’s exit status conveys information to the program that invoked it. Use the exit statement from within an awk program to set the exit status.
gawk allows you to include other awk source files into your program using the @include statement and/or the -i and -f command-line options.
gawk allows you to load additional functions written in C or C++ using the @load statement and/or the -l option. (This advanced feature is described later, in Writing Extensions for gawk.)