Cameron Simpson wrote: > On 14Sep2008 23:50, Kevin Martin <kevintm@xxxxxxxxxxxxx> wrote: > | So I'm fairly confused at this point. > | > | Start with a /bin/sh shell. > | > | Then do: > | > | sh-3.2$ unset $? > | sh: unset: `0': not a valid identifier > | > | ok, no problem; then do > | > | sh-3.2$ /bin/ksh -c " set -xv ; grep ABCD b ; echo $? ; if [ "$?" = > | "0" ] ; then echo yes ; fi" > > You know you need to escape " inside ", yes? As it happens it has no > effect in your script here, but ... > > | + grep ABCD b > | ABCD="C" ; export ABCD > | + echo 1 > | 1 > | + [ 1 = 0 ] > | > | WHAT? > > The "echo" command has a return status, and trashes your $?. > > | Then do it again without unsetting $?: > > You don't ever unset $?. It is not a meaningful idea. > > If you want a particular $?, do this: > > grep ABCD b > xit=$? > echo $xit # overwrites $?, but $xit is untouched > if [ $xit = 0 ] > then > ... > > but almost invariably when someone does: > > some_command ... > if [ $? = 0 ] > then > > they would be MUCH better off just going: > > if some_command ... > then > > Remember that the predicate in an if/while if a command_list, and the > exit status of the last command in the command_list is what is tested. > The command "[" (aka "test") is just another command suited to simple > Boolean tests. But it is not "special". > > Example: > > # repeat prompt until EOF or empty reply > while echo "Enter something:" > read foo && [ -n "$foo" ] > do > echo "foo=$foo" > done > > | [...snip...] Is this a ksh bug? > > No. > > Cheers, > Uh, yeah, duh on my part on the "unset $?" stupidity. I was trying to duplicate what I'm seeing in our application. Essentially we have an application that can run remote commands on a schedule (kind of like a network scron) and it basicly execs a "/bin/sh" and runs whatever command you've passed it. What I've been seeing is if I try to pass the "/bin/ksh -c "if...."" script the $? of the grep never seems to be 0 for some reason so I essentially get the results that I showed in my example where I was doing the dumb "unset $?" (making, at that point, $? = 1). I agree that the "if some_command" would be a much better way of doing this but I get the same results if I do that as I do if I do the "some_command" the "if [ $? = 0 ]" test. From reading the man page for ksh I may be running into a POSIX vs non-POSIX issue. Kevin -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list Guidelines: http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
