Path: utzoo!utgpu!water!watmath!clyde!rutgers!sri-spam!ames!aurora!labrea!decwrl!sun!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.unix.questions
Subject: Re: Using pipes within awk programs
Summary: Described in AWK book.
Keywords: awk, pipe
Message-ID: <537@cresswell.quintus.UUCP>
Date: 15 Jan 88 00:51:12 GMT
References: <515@root44.co.uk>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 47

In article <515@root44.co.uk>, gwc@root.co.uk (Geoff Clare) ask
about using pipes within awk programs.

This feature is described in the book
	The AWK Programming Language
	Aho, Kernighan, & Weinberger
	Addison-Wesley
	ISBN 0-201-07981-X
	US$ 22

Page 62 (The getline function):
	Cmd | getline		-- sets $0 and NF
	Cmd | getline Var	-- sets Var
The command is executed ONCE, just as a <file in that position
is opened ONCE.  All forms of getline return
	-1 if an error occurred
	 0 if end of file was encountered
	 1 if a record was read

Page 58 (Output into Pipes):
	print Stuff | Command
	printf(Format,Exprs) | Command
The command is executed ONCE, just as a >File in that position
is opened ONCE.

Page 59 (Closing Files and Pipes):
	close("...")
closes a pipe or a file.

BEWARE:  files and pipes share a name space.  That is, if AWK
sees
	print Entry >>"cat"
it will open a FILE called "cat" and from then on "cat" will
designate that file.  But if it sees
	print Remark | "cat"
it will open a PIPE, and from then on "cat" will designate that
pipe.  close("cat") will close either a file or a pipe, depending
on what the string was associated with.  Avoid file names that
look like commands.

In SunOS 3.2,	print | "cmd" works
	  but	"cmd" | getline doesn't.

Anyone who is interested in mastering AWK should at least read this
book.  It describes the latest version, so there are some features
(like user-defined functions, alas) which may not be available in
the version you're using.  The latest version is available for MS-DOS...