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From: dce@mips.UUCP
Newsgroups: comp.unix.questions
Subject: Re: Quotiing * in Bourne shell question
Message-ID: <417@quacky.UUCP>
Date: Fri, 22-May-87 10:37:14 EDT
Article-I.D.: quacky.417
Posted: Fri May 22 10:37:14 1987
Date-Received: Sat, 23-May-87 10:47:45 EDT
References: <1040@chinet.UUCP> <1028@mips.UUCP>
Reply-To: dce@quacky.UUCP (David Elliott)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 96

In article <1028@mips.UUCP> hitz@mips.UUCP (David Hitz) writes:
>In article <1040@chinet.UUCP> megabyte@chinet.UUCP (Dr. Megabyte) writes:
>>
>>I want to set a shell variable equal to an asterix (*). Then use that
>>variable in seetting another shell variable and then finally use the 
>>second variable as a command line with the asterix NOT being expanded,
>>I want it passed to the program.  Here is an example:
>
>This is probably the best:
>
>	area="*"		
>	cmdline="echo foo '$area' bar" 
>	eval $cmdline 			

The last line should be

	eval "$cmdline"

to prevent the shell from eating any other special characters. In this
case, there are none, but we should try to handle them all.

The general rule is: Always put double quotes around variables unless
you know exactly what's in the variable and know it can't hurt you.
If you can't know the values beforehand, you can check them. The
following shell script takes two arguments: the new IFS (a null one uses
the default) and the value to be checked. It prints a message saying
whether or not the value contains the IFS characters:


	#!/bin/sh
	case "$1" in
		"")
			;;
		*)
			IFS="$1"
			;;
	esac
	case "$2" in
		*["$IFS"]*)
			echo "$2 has IFS($IFS) in it"
			;;
		*)
			echo "$2 OK"
			;;
	esac

Best of all, the checking doesn't cost a single fork (the "echo"
statements cost on most BSD systems, but that's not part of the
check, per se).

Anyway, to get back to the original problem:

	#!/bin/sh

	area="*"					# set area to *
	cmdline="acego -q ovt.rpt $area" 		# run report
	$cmdline | lp -dDS180 				# to lp in 1215
	exit 0						# Bye-bye

This should be

	#!/bin/sh
	area="*"
	cmdline="acego -q ovt.rpt '$area'"
	eval "$cmdline" | lp -dDS180

except that if $area could be set by the user, it could conceivably
contain single quotes. I think that the following is the best solution
(and I know that Dave Hitz will tell me if it isn't):

	#!/bin/sh
	area={some value}
	...

	case "$area" in
		*"'"*)
			area=`echo "$area" | sed 's/'"'"'/'"'"'"'"'"'"'"'"'/g'`
			;;
	esac
	cmdline="acego -q ovt.rpt '$area'"
	eval "$cmdline" | lp -dDS180

Again, it only costs an extra fork in the extreme case.

In case you are baffled, the sed script is actually

	s/'/'"'"'/

which changes a value of x'y to x'"'"'y, which, when surrounded by single
quotes is 'x'"'"'y', which, when processed by the shell, is passed to
sub-commands as x'y.

It's all clear as mud.
-- 
David Elliott		{decvax,ucbvax,ihnp4}!decwrl!mips!dce
"With an a) like that, you've got a lot of nerve asking for a b)!"-P. Schaeffer