Conventions (The GNU Awk User’s Guide)
This Web page is written in Texinfo, the GNU documentation formatting language. A single Texinfo source file is used to produce both the printed and online versions of the documentation. Because of this, the typographical conventions are slightly different than in other books you may have read.
Examples you would type at the command line are preceded by the common shell primary and secondary prompts, ‘
$’ and ‘
>’, respectively. Input that you type is shown like this. Output from the command is preceded by the glyph “-|”. This typically represents the command’s standard output. Error messages and other output on the command’s standard error are preceded by the glyph “error→”. For example:
$ echo hi on stdout -| hi on stdout $ echo hello on stderr 1>&2 error→ hello on stderr
In the text, almost anything related to programming, such as command names, variable and function names, and string, numeric and regexp constants appear in
this font. Code fragments appear in the same font and quoted, ‘
like this’. Things that are replaced by the user or programmer appear in
this font. Options look like this:
-f. File names are indicated like this:
/path/to/ourfile. Some things are emphasized like this, and if a point needs to be made strongly, it is done like this. The first occurrence of a new term is usually its definition and appears in the same font as the previous occurrence of “definition” in this sentence.
Characters that you type at the keyboard look like this. In particular, there are special characters called “control characters.” These are characters that you type by holding down both the CONTROL key and another key, at the same time. For example, a Ctrl-d is typed by first pressing and holding the CONTROL key, next pressing the d key, and finally releasing both keys.
For the sake of brevity, throughout this Web page, we refer to Brian Kernighan’s version of
awk as “BWK
awk.” (See section Other Freely Available awk Implementations for information on his and other versions.)
Dark corners are basically fractal—no matter how much you illuminate, there’s always a smaller but darker one.
— Brian Kernighan
Until the POSIX standard (and GAWK: Effective AWK Programming), many features of
awk were either poorly documented or not documented at all. Descriptions of such features (often called “dark corners”) are noted in this Web page with “(d.c.).” They also appear in the index under the heading “dark corner.”
But, as noted by the opening quote, any coverage of dark corners is by definition incomplete.
Extensions to the standard
awk language that are supported by more than one
awk implementation are marked “(c.e.),” and listed in the index under “common extensions” and “extensions, common.”