Effective awk Programming, 4th Edition

Chapter 2. Running awk and gawk

This chapter covers how to run awk, both POSIX-standard and gawk-specific command-line options, and what awk and gawk do with nonoption arguments. It then proceeds to cover how gawk searches for source files, reading standard input along with other files, gawk’s environment variables, gawk’s exit status, using include files, and obsolete and undocumented options and/or features.

Many of the options and features described here are discussed in more detail later in the book; feel free to skip over things in this chapter that don’t interest you right now.

Invoking awk

There are two ways to run awk—with an explicit program or with one or more program files. Here are templates for both of them; items enclosed in [...] in these templates are optional:

awk [options] -f progfile [--] file … awk [options] [--] 'program' file …

In addition to traditional one-letter POSIX-style options, gawk also supports GNU long options.

It is possible to invoke awk with an empty program:

awk '' datafile1 datafile2

Doing so makes little sense, though; awk exits silently when given an empty program. (d.c.) If --lint has been specified on the command line, gawk issues a warning that the program is empty.

Command-Line Options

Options begin with a dash and consist of a single character. GNU-style long options consist of two dashes and a keyword. The keyword can be abbreviated, as long as the abbreviation allows the option to be uniquely identified. If the option takes an argument, either ...