Re: strange shell behavior...thoughts?

[Ed Greshko <Ed Greshko greshko com>]

Kevin Martin 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"
> + grep ABCD b
> ABCD="C" ; export ABCD
> + echo 1
> 1
> + [ 1 = 0 ]
>
> WHAT? 
>
> Then do it again without unsetting $?:
> sh-3.2$ /bin/ksh -c " set -xv  ; grep ABCD b ; echo $? ; if [ "$?" = "0"
> ] ; then echo yes ; fi"
> + grep ABCD b
> ABCD="C" ; export ABCD
> + echo 0
> 0
> + [ 0 = 0 ]
> + echo yes
> yes
>
>
> Why doesn't the first iteration work?  Is this a ksh bug?
>
>
>   
I don't think you are testing what you think you are testing....

I believe that when you execute "ksh -c" you won't get a return value
for the commands in the string as you have them listed.

Take the 3 potential return codes for grep.

0 = string found
1 = string not found
2 = file not found

$ cat b
ABCD
$ grep ABCD b
ABCD
$ echo $?
0
$ grep K b
$ echo $?
1
$ grep ABCD kkk
grep: kkk: No such file or directory
$ echo $?
2

$ ksh -c "set -xv ; grep ABCD kkk ; echo $?"
+ grep ABCD kkk
grep: kkk: No such file or directory
+ echo 0
0

Clearly the "echo $?" is not returning the code from grep...but from the
last command of the parent shell...

As in....

$ grep ABCD kkk
grep: kkk: No such file or directory
$ ksh -c "set -xv ; grep ABCD kkk ; echo $?"
+ grep ABCD kkk
grep: kkk: No such file or directory
+ echo 2
2

I don't do much shell scripting these days....but it may not even be the
result of "ksh -c" it could just be what is true when you use ";" to
string commands together on the same line.


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