-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 According to Dave Korn on 8/14/2009 7:11 AM: >> a="`""`" >> >> is non-portable, but can always be replaced by the portable: >> >> a=`""` >> >> See why I don't like spurious "" around variable assignments? > > Ah, now I do. Ok, but is some nice clear list of where you should and > shouldn't quote anywhere? As far as I can tell you have to memorize the > entire bash manual and then infer what to do from all the overlapping sets of > expansions and contexts and rules. Then you have to to the same for all the > other shells we're supposed to support. Then you have to infer a set of > lowest-common-denominator rules from all of that.
I think it's as simple as: if you are doing variable assignment, there is no word splitting, so you only need quotes if it would otherwise look like multiple words: a=$1 b="$1 $2" if you are doing case statements, there is no word splitting, so you only need quotes if it would otherwise look like multiple words: case $1 in case " $1 " in if you are doing `` which needs embedded quoting, then it is only safe to do it as variable assignment (where `` looks like a single word, without needing outer ""): a=`echo "$1 $2"` pretty much every where else, all $ expansions need double quotes if you want to avoid word splitting (but using $ expansions to hide tool names is one case where you DO want word splitting): ECHO='printf %s\n' $ECHO "$1" And beyond that, it's just lots of practice. I agree that it often feels like you have to memorize loads of information to write portable shell, but at least these public reviews catch a lot of the pitfalls. - -- Don't work too hard, make some time for fun as well! Eric Blake e...@byu.net -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkqFYVAACgkQ84KuGfSFAYBIRwCgxRt0p2lnFnSfQOHl0TR1puou rPoAoJsTLkaB4QMg6ZcTsD2bKqNWftfQ =wagC -----END PGP SIGNATURE-----
