strange shell behavior...thoughts?

[Cameron Simpson]

On 14Sep2008 23:50, Kevin Martin <kevintm at ameritech.net> 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,
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

The first ninety percent of the task takes ninety percent of the time, and
the last ten percent takes the other ninety percent.