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From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.questions
Subject: Re: use of set in a shell script
Message-ID: <5119@solo5.cs.vu.nl>
Date: 17 Jan 90 23:15:03 GMT
References: <472@cpsolv.UUCP> <5060@solo9.cs.vu.nl> <1197@root44.co.uk>
Reply-To: maart@cs.vu.nl (Maarten Litmaath)
Organization: VU Informatika, Amsterdam, the Netherlands
Lines: 77

In article <1197@root44.co.uk>,
	gwc@root.co.uk (Geoff Clare) writes:
\In article <5060@solo9.cs.vu.nl> maart@cs.vu.nl (Maarten Litmaath) writes:
\>optc=0
\>optv=
\>
\>for i
\>do
\>	case $i in
\>	-*)
\>		optc=`expr $optc + 1`
\>		eval optv$optc='"$i"'
\>		optv="$optv \"\$optv$optc\""
\>		;;
\>	*)
\>		# you get the idea
\>	esac
\>done
\>
\>eval set $optv		# restore the options EXACTLY
\
\A good attempt, Maarten, but there are a couple of big problems here.  

A good attempt, Geoff, but there ... :-)

\Firstly, the use of "expr" will be extremely slow for shells which don't
\have "expr" built in (virtually all Bourne shells, I think).  There's no
\need to use a separate variable for each argument, anyway.

Wrong.  I didn't do that for nothing, you know.  See below.

\Secondly, the final "set" command will not work correctly.  Suppose at
\the start of the script $1 contains "-x".  This will end up as a
\"set -x" command, which will turn on tracing mode in the shell, not
\place "-x" in $1.  With some shells you can use "--" in a "set" command
\to mark the end of the options, but a dummy first argument is more
\portable.  [...]

You're right on this one.  In fact I meant to include a `-':

	eval set - $optv

\	case $i in
\	-*)
\		optv="$optv '$i'"
\...

What if $i were

	-'

(sic)?  Ridiculous, I know, but we're talking foolproof here.
The extra level of variables is one way to deal with nasty arguments, here's
another:

        case $i in
        -*\'*)   
                tmp=`echo x"$i" | sed -e 's/.//' -e "s/'/'\\\\\\\\''/g"`
                optv="$optv '$tmp'" 
                ;; 
        -*)      
                optv="$optv '$i'"
                ;; 
        esac

BTW, I tested this under SunOS 4.0.3c.
But wait a minute!  There's another problem: what if $i contains C escape
sequences and one is using that terrible System-V echo...? :-(
Hmm, one could always use the portable echo hack:
----------8<----------8<----------8<----------8<----------8<----------
: 'portable echo hack: do not interpret backslash escape sequences'
cat << EOF
$*
EOF
-- 
  What do the following have in common:  access(2), SysV echo, O_NONDELAY?  |
  Maarten Litmaath @ VU Amsterdam:  maart@cs.vu.nl,  uunet!mcsun!botter!maart