[Server-devel] Fixing bash script bogosity - help?

[pgf at laptop.org]

andrew wrote:
 > On Tue, 2009-04-28 at 23:25 +1200, Andrew McMillan wrote:
 > > Hi Martin,
 > > 
 > > Perhaps:
 > > 
 > > =========================================
 > > #!/bin/bash -x
 > > 
 > > [ -n "$DEBUG" ] && set -o xtrace
 > > 
 > > declare -a inparms
 > > 
 > > declare -i i=0
 > > while true; do
 > >   inparms[$i]="${1/\"/\\\"}" 
 > 
 > Sorry, that should have read:
 > 
 >     inparms[$i]="${1//\"/\\\"}"
 > 
 > so that all instances of " were replaced by \", rather than just the
 > first one :-)

i went down a similar path and even sent martin a modified
version of his script before realizing the general case is much
worse than that.  you have to deal with escaping existing
backslashes, and single quotes, and i think all of the other
special shell characters as well.

the one bright spot of the exercise (if you can call it that) was
that in re-learing the pattern subustitution thing, i found that
you can do that "ugly hack" pattern replacement without the
surrounding loop, because it can be applied to all elements of an
array at once:
	newARGS=( "${ARGS[@]//\"/\\\"}" )

small pleasures, i know.

(i didn't retest that, but it's close.)

paul

 > 
 > Cheers,
 > 					Andrew.
 > 
 > >   shift || break
 > >   i=$(( $i + 1 ))
 > > done
 > > 
 > > printargs() {
 > >   local -i j=0
 > >   while [ $j -lt $i ] ; do
 > >     printf ' "%s"' "${inparms[$j]}"
 > >     j=$(( $j + 1 ))
 > >   done
 > > }
 > > 
 > > # in the script, the CMD is built up as a string
 > > CMD="touch `printargs`"
 > > 
 > > # in practice we somtimes use /sbin/runuser -c
 > > # and other times plain bash -c
 > > bash -c "$CMD"
 > > 
 > > =========================================
 > > 
 > > Line 9 is an ugly hack, and quite possibly a bashism.
 > > 
 > > 
 > > Hope this is some use,
 > > 
 > > 					Andrew McMillan.
 > > 
 > > 
 > > On Mon, 2009-04-27 at 22:37 +0200, Martin Langhoff wrote:
 > > > Hi all,
 > > > 
 > > > I have a simple shell scripting problem :-) you'll find attached a
 > > > shell script that ships with ejabberd. It is a fairly straightforward
 > > > bit of code, and allows us to control bits of the ejabberd internals
 > > > with a nice cli interface. (Feel free to skip the start / stop bits of
 > > > the code, I'm fighting with the ctrl function.)
 > > > 
 > > > The problem it has is that the parameters are passed to a bash or
 > > > runas invocation -- at which point the quoting is a mess. Currently I
 > > > am working around it in the caller by doing some stupid
 > > > nested-quoting. But this should be easy to cure -- if anyone knows a
 > > > bit more bash (or portable shell!) than me :-)
 > > > 
 > > > A minimal exposition of the problem is as follows:
 > > > 
 > > > $ cat sample.sh
 > > > #!/bin/bash -x
 > > > 
 > > > # in the script, the CMD is built up as a string
 > > > CMD="touch $@"
 > > > # in practice we somtimes use /sbin/runuser -c
 > > > # and other times plain bash -c
 > > > bash -c "$CMD"
 > > > 
 > > > # this invokation does the wrong thing -
 > > > $ ./sample.sh ./sample.sh "this is file one" "this is file two"
 > > > # the ugly workaround is
 > > > ./sample.sh "'this is file one'" "'this is file two'"
 > > > 
 > > > Any hints that don't involve a rewrite?
 > > > 
 > > > cheers,
 > > > 
 > > > 
 > > > 
 > > > martin-who's-easily-stumped-with-shell-backwardnesss
 > > 
 > > ------------------------------------------------------------------------
 > > andrew (AT) morphoss (DOT) com                            +64(272)DEBIAN
 > >  You will be awarded a medal for disregarding safety in saving someone.
 > > ------------------------------------------------------------------------
 > > 
 > > 
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 > > 
 > ------------------------------------------------------------------------
 > andrew (AT) morphoss (DOT) com                            +64(272)DEBIAN
 >    You have the power to influence all with whom you come in contact.
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=---------------------
 paul fox, pgf at laptop.org