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From: jerryp@tektools.UUCP (Jerry Peek)
Newsgroups: net.unix
Subject: Re: You can pass *anything* to awk: even in BEGIN!
Message-ID: <1597@tektools.UUCP>
Date: Wed, 24-Sep-86 12:07:47 EDT
Article-I.D.: tektools.1597
Posted: Wed Sep 24 12:07:47 1986
Date-Received: Fri, 26-Sep-86 18:50:15 EDT
References: <198@comp.lancs.ac.uk> <753@moscom.UUCP> <7754@lanl.ARPA> <185@motown.UUCP>
Reply-To: jerryp@tektools.UUCP (Jerry Peek)
Distribution: net
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 67

In article <185@motown.UUCP> jmr@motown.UUCP (John M. Ritter) writes:
> awk '
> BEGIN { TERM = "'$TERM'";	# From Environment
> 	VAR1 = "'$VAR1'";	# From Above
> 	VAR2 = "'"$VAR2"'";	# From Above: Note strange quotes!
   ...etc...
>       } # End of BEGIN
>
> This method DOES allow initialization within the BEGIN block, and it is
> also as easy to use as $1 in a shell script...
> 
> I can't think of anything that has been left out. This is using
> System V, r2.0v2 - I'd love to know if this works on other versions
> of Unix.

Seems like this should work everywhere (unless I'm missing something?); it's
dependent on the quoting behavior of the *shell*, not awk.  You just have to
make sure that the shell plugs in the values before it invokes "awk".

I've been taking this a step farther, to let me define arbitrary variables
(or array members) within an "awk" BEGIN block.  First, I write a
shell script which outputs strings of the form:

	VAR = "some junk"
	array["member 1"] = "VALUE 1"
	array["member 2"] = "VALUE 2"

... these are the variable-assignment commands you want "awk" to do.
(They might include things that vary, day-to-day, like the output of "date"
or "who" or "uptime" or...)  Let's call that program "mkawkvars".

Then, you put the "mkawkvars" output into your awk script.  Use the shell's
command-substitution feature (backquotes or grave accents), like this:

	awk "
	BEGIN { `mkawkvars`"' }
	{
	     ...rest of awk script...
	}'

The quoting is important.  The first section of the script has doublequotes (")
around it.  That's because:

	- the command-substitution (`mkawkvars`) won't work if you enclose it
	  within singlequotes('`mkawkvars`').

	- the mkawkvars script must output newlines after every
	  variable-assignment command.  If you don't quote the 
	  mkawkvars output at all, the newlines disappear; awk
	  will see all the variable assignments on one line, like this:

		VAR = "some junk" array["member 1"] = "VALUE 1" array[...

	  ... causing "awk: bailing out near line 2..." :-)

You can surround the first part of the BEGIN block with doublequotes, then
switch to singlequotes (as I did above) after `mkawkvars` has been executed.

This article is too long already, so I won't include any more examples.
If anyone's interested, though, send me mail and I'll send you a copy
of a working script.

--Jerry Peek, Tektronix, Inc.
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